Publication List

47. "Dielectrophoretic monitoring and inter-strain separation of intact Clostridium difficile based on their S(surface)-layers", Y.-H. Su, C. Warren, R.L. Guerrant, N.S. Swami*; Anal Chem (2014), 86, 10855–10863, Journal Impact Factor = 5.8; DOI: 10.1021/ac5029837 Download
Nathan Swami
The role of the human microbiota in health and disease has become increasingly apparent. However, characterizing microbial to microbial and polymicrobial population to host interactions has been challenging. Clostridium difficile infection (CDI), the single most common cause of antibiotic-induced enteric infection that is associated with increased morbidity and in-hospital fatalities, is a perfect example. Inter-strain antagonistic interactions across the host microbiome form an important strategy for controlling the emergence of CDI. The current diagnosis method for CDI, based on immunoassays for toxins produced by pathogenic C.difficile strains, is limited by false negatives due to rapid toxin degradation. Furthermore, simultaneous monitoring of non-toxigenic C.difficile strains is not possible, due to absence of these toxins, thereby limiting its application towards the control of CDI through optimizing antagonistic inter-strain interactions. Herein, we demonstrate that morphological differences within the cell wall of particular C.difficile strains with differing S-layer proteins can induce systematic variations in their electrophysiology, due alterations in cell wall capacitance. As a result, dielectrophoretic frequency analysis can enable the independent fingerprinting and label-free separation of intact microbials of each strain type from mixed C.difficile samples. The sensitivity of this contact-less electrophysiological method is benchmarked against the immunoassay and microbial growth rate methods for detecting alterations within both, toxigenic and non-toxigenic C.difficile strains after vancomycin treatment. This microfluidic diagnostic platform can assist in the development of therapies for arresting clostridial infections by enabling the isolation of individual strains, optimization of antibiotic treatments and the monitoring of microbiomes.

46. "Quantifying spatio-temporal dynamics of biomarker pre-concentration and depletion in microfluidic systems by intensity threshold analysis", A. Rohani, W. Varhue, Y.-H. Su, N. S. Swami; Biomicrofluidics (2014) 8, 052009. Journal Impact Factor =3.8 Journal Impact Factor = 3.8; Download
Nathan Swami
Microfluidic systems are commonly applied towards pre-concentration of biomarkers for enhancing detection sensitivity. Quantitative information on the spatial and temporal dynamics of pre-concentration, such as its position, extent and time evolution are essential towards sensor design for coupling pre-concentration to detection. Current quantification methodologies are based on the time evolution of fluorescence signals from biomarkers within a statically defined region of interest, which does not offer information on the spatial dynamics of pre-concentration and leads to significant errors when the pre-concentration zone is delocalized or exhibits wide variations in size, shape and position over time under the force field. We present a dynamic methodology for quantifying the region of interest by using a statistical description of particle distribution across the device geometry to determine the intensity thresholds for particle pre-concentration. This method is applied to study the delocalized pre-concentration dynamics under an electrokinetic force balance driven by negative dielectrophoresis, for aligning the pre-concentration and detection regions of neuropeptide Y, and for quantifying the polarizability dispersion of silica nano-colloids with frequency of the force field. We envision the application of this automated methodology on data from 2D images and 3D Z-stacks for quantifying pre-concentration dynamics over delocalized regions as a function of the force field.

45. “Wide bandwidth power amplifier for frequency-selective insulator-based dielectrophoresis”, Farmehini, V., Rohani, A., Su, Y. H., & Swami, N.*; Lab Chip (2014) DOI: 10.1039/C4LC00801D. Journal Impact Factor = 5.75; Download
Nathan Swami
Insulator-based dielectrophoresis enables contact-less separation and analysis of biosystems, but it is unable to operate effectively in the MHz frequency range, which is necessary for the manipulation of biological cells based on the characteristic electrophysiology of their cytoplasm or biomolecular preconcentration based on their unique conformation. To address the steep drop in output power and the rise of signal distortions within conventional amplifiers at MHz frequencies due to slew rate limitations, we present the design principles for a wideband amplifier. This is validated by demonstrating the absence of harmonic distortions and parasitic DC within the amplifier output up to 15 MHz, thereby enabling analysis of cytoplasmic alterations on oocysts of Cryptosporidium parvum, due to constant force dispersion in the MHz range.

44. “Electrical tweezer for highly parallelized electrorotation measurements over a wide frequency bandwidth”, Rohani, A., Varhue, W., Su, Y. H., & Swami, N. S.*; Electrophoresis (2014) DOI: 10.1002/elps.201400021 Journal Impact Factor = 3.16; Download
Nathan Swami
Electrorotation (ROT) is a powerful tool for characterizing the dielectric properties of cells and bioparticles. However, its application has been somewhat limited by the need to mitigate disruptions to particle rotation by translation under positive DEP and by frictional interactions with the substrate. While these disruptions may be overcome by implementing particle positioning schemes or field cages, these methods restrict the frequency bandwidth to the negative DEP range and permit only single particle measurements within a limited spatial extent of the device geometry away from field nonuniformities. Herein, we present an electrical tweezer methodology based on a sequence of electrical signals, composed of negative DEP using 180-degree phase-shifted fields for trapping and levitation of the particles, followed by 90-degree phase-shifted fields over a wide frequency bandwidth for highly parallelized electrorotation measurements. Through field simulations of the rotating electrical field under this wave-sequence, we illustrate the enhanced spatial extent for electrorotation measurements, with no limitations to frequency bandwidth. We apply this methodology to characterize subtle modifications in morphology and electrophysiology of Cryptosporidium parvum with varying degrees of heat treatment, in terms of shifts in the electrorotation spectra over the 0.05–40 MHz region. Given the single particle sensitivity and the ability for highly parallelized electrorotation measurements, we envision its application toward characterizing heterogeneous subpopulations of microbial and stem cells.

43. “Nanomaterial-based electrochemical sensing of neurological drugs and neurotransmitters”, Sanghavi, B. J., Wolfbeis, O. S., Hirsch, T., & Swami, N. S. *; Microchimica Acta (2014), 1-41. Journal Impact Factor = 3.72; Download
Nathan Swami
Nanomaterial-modified detection systems represent a chief driver towards the adoption of electrochemical methods, since nanomaterials enable functional tunability, ability to self-assemble, and novel electrical, optical and catalytic properties that emerge at this scale. This results in tremendous gains in terms of sensitivity, selectivity and versatility. We review the electrochemical methods and mechanisms that may be applied to the detection of neurological drugs. We focus on understanding how specific nano-sized modifiers may be applied to influence the electron transfer event to result in gains in sensitivity, selectivity and versatility of the detection system. This critical review is structured on the basis of the Anatomical Therapeutic Chemical (ATC) Classification System, specifically ATC Code N (neurotransmitters). Specific sections are dedicated to the widely used electrodes based on the carbon materials, supporting electrolytes, and on electrochemical detection paradigms for neurological drugs and neurotransmitters within the groups referred to as ATC codes N01 to N07. We finally discuss emerging trends and future challenges such as the development of strategies for simultaneous detection of multiple targets with high spatial and temporal resolutions, the integration of microfluidic strategies for selective and localized analyte pre-concentration, the real-time monitoring of neurotransmitter secretions from active cell cultures under electro- and chemotactic cues, aptamer-based biosensors, and the miniaturization of the sensing system for detection in small sample volumes and for enabling cost savings due to manufacturing scale-up. The Electronic Supporting Material (ESM) includes review articles dealing with the review topic in last 40 years, as well as key properties of the analytes, viz., pKa values, half-life of drugs and their electrochemical mechanisms. The ESM also defines analytical figures of merit of the drugs and neurotransmitters. The article contains 198 references in the main manuscript and 207 references in the Electronic Supporting Material.

42. “Electrokinetic preconcentration and detection of neuropeptides at patterned graphene-modified electrodes in a nanochannel”, Sanghavi, B. J., Varhue, W., Chávez, J. L., Chou, C. F., & Swami, N. S.*; Analytical chemistry, 86(9), 4120-4125. Journal Impact Factor = 5.83; Download
Nathan Swami
Neuropeptides are vital to the transmission and modulation of neurological signals, with Neuropeptide Y (NPY) and Orexin A (OXA) offering diagnostic information on stress, depression, and neurotrauma. NPY is an especially significant biomarker, since it can be noninvasively collected from sweat, but its detection has been limited by poor sensitivity, long assay times, and the inability to scale-down sample volumes. Herein, we apply electrokinetic preconcentration of the neuropeptide onto patterned graphene-modified electrodes in a nanochannel by frequency-selective dielectrophoresis for 10 s or by electrochemical adsorptive accumulation for 300 s, to enable the electrochemical detection of NPY and OXA at picomolar levels from subnanoliter samples, with sufficient signal sensitivity to avoid interferences from high levels of dopamine and ascorbic acid within biological matrices. Given the high sensitivity of the methodology within small volume samples, we envision its utility toward off-line detection from droplets collected by microdialysis for the eventual measurement of neuropeptides at high spatial and temporal resolutions.

41. “Quantitative dielectrophoretic tracking for characterization and separation of persistent subpopulations of Cryptosporidium Parvum”, Y. –H. Su, M. Tsegaye, W. Varhue, K. T. Liao+, L. Abebe, J. A. Smith, R. L. Guerrant, N. S. Swami*; Analyst (2014) 139, 66-73. Journal Impact Factor = 3.9; Invited Cover Article & listed as: “Hot Article”. Download
Nathan Swami
Microbial persistence to antibiotics is attributed to subpopulations with phenotypic variations that cause a spread of susceptibility levels, leading to the recurrence of infections and stability of biofilms. Herein, persistent oocyst subpopulations of Cryptosporidium parvum, a water-borne pathogen causing enteric infections, are separated and characterized by quantitative dielectrophoretic tracking over a wide frequency range (10 kHz – 10 MHz), by utilizing differences in magnitude and direction of trapping force.

40. “Disinfection action of electrostatic versus steric-stabilized silver nanoparticles on E. Coli”, E. Fauss, E. MacCusppie, V. Carver, J. A. Smith, N. S. Swami*, Colloids & Surfaces B: Biointerfaces (2014), 113, 77-84. Journal Impact Factor = 3.5. Download
Nathan Swami
The capping layer stabilizing silver nanoparticles (AgNPs) affects its aggregation, dissolution, and net disinfection action, especially under conditions of varying water composition. Herein, we correlate the silver ion (Ag+) release and reactive oxygen species (ROS) generation rates for electrostatic versus steric stabilized AgNPs to their net disinfection coefficient on E. coli, under differing water chemistries. Steric stabilization of AgNPs enables disinfection within a range of water chemistries, whereas effective disinfection can occur under electrostatic stabilization, only at low salt and organic matter levels.

39. "Enhanced penetration of fluoride particles into bovine enamel through combining AC electro-osmosis with dielectrophoresis”, C. Ivanoff, N.S. Swami, T. Hottel, F. Godoy-Garcia. Electrophoresis (2013) Journal Impact Factor = 3.3. DOI: 10.1002/elps.201300206
Nathan Swami
Fluoride deposition into the pores of enamel is necessary at high concentrations to reduce enamel demineralization and with a high degree of penetration to account for loss by ingestion. Current diffusion and electrochemical methods are inadequate for effectively transporting fluoride greater than 20 μm into enamel. The study explores the coupling of frequency-modulated dielectrophoresis (DEP) and AC electroosmosis (ACEO) to selectively concentrate fluoride particles from fluoride gel excipients and enhance their penetration into enamel.

38. “Real-time electrochemical monitoring of ATP at graphene-modified electrodes”, B. Sanghavi, S. Sitaula, M. Griep, S. Karna, M. Ali, N. S. Swami* Anal. Chem. (2013), 85, 8158–8165 Journal Impact Factor =5.7. Download
Nathan Swami
We report on a competitive electrochemical detection system that is free of wash-steps and enables the real-time monitoring of adenosine triphosphate (ATP) over a five-log concentration range, with the ability to speed-up target binding kinetics by increasing capture probe concentration.

37. “Scaling down constriction-based dielectrophoresis for trapping nanoscale biomolecules in high conductivity media”, V. Chaurey, A. Rohani, Y.-H. Su, W. Varhue, K.T. Liao, C. F. Chou, N. S. Swami*, Electrophoresis (2013), 34, 1097-1104. Journal Impact Factor =3.3 Download
Nathan Swami
Selective trapping of nanoscale bio-particles (size < 100 nm) is significant for the separation and high-sensitivity detection of biomarkers. Dielectrophoresis is capable of highly selective trapping of bio-particles based on their characteristic frequency response. However, the trapping forces fall steeply with particle size, especially within physiological media of high-conductivity where the trapping can be dissipated by electrothermal flow due to localized Joule heating. Herein, we investigate the influence of device scaling within the electrodeless insulator dielectrophoresis geometry through the application of highly constricted channels of successively smaller channel depth, on the net balance of dielectrophoretic trapping force versus electrothermal drag force on bio-particles.

36. “Integrating Ethics and Policy Into Nanotechnology Education”, Gorman, M.E.; Swami, N.; Cohoon, J.M.G.; Groves, J.; Squibbs, K.; Werhane, P.H.; Journal of Nano Education, (2012), 4 (1-2), 1-2. Journal Impact Factor =1.5;

35. “Nanofiber size-dependent sensitivity of fibroblast directionality to the methodology for scaffold alignment”, V. Chaurey, F. Block, R. Su, P. Chiang, E.A. Botchwey, C.F. Chou, N. Swami*, Acta Biomaterialia (2012), 8, 3982–3990. Journal Impact Factor = 4.865. Download
Nathan Swami
The sensitivity of fibroblast guidance to the directional cues provided by aligned nanofibers is studied for scaffolds of successively smaller fiber sizes fabricated using mandrel and electrical alignment methodologies for electrospun nanofibers, as well as nano-imprint methodologies for perfectly aligned fibers. On aligned scaffolds of large fibers (~740 nm), cell directionality closely follows the underlying fibers, irrespective of the alignment method. However, on scaffolds with sub-100 nm fiber size, the cell directionality can be maintained in the range of nanofiber alignment deviations, only with electrically aligned methods, since the polarization provides molecular-scale directional adhesion cues to cell receptors.

34. “Photoelectrochemical Performance of Electrodeposited Cu2O on TiO2 Nanotubes”, Tsui, Lok-kun; Wu, Lingling; Swami, Nathan S. ; Zangari, Giovanni*. Electrochemistry Letters (2012), 1 (2), D15-D19. Journal Impact Factor =1.84; Download
Nathan Swami
The titania (TiO2) nanotube system has broad potential for photoelectrochemical solar cell applications, but its conversion efficiency is limited by the wide 3.2 eV bandgap. We demonstrate a significant improvement of the photoelectrochemical performance of the nanotubes by extending absorption into the visible spectrum via modification with electrodeposition of cuprous oxide. Using a 3-step pulse electrodeposition technique to optimize the morphology and doping type of the cuprous oxide, we show a fourfold enhancement in photoelectrochemical conversion efficiency.

33. “Nano-constriction device for rapid protein pre-concentration in physiological media by electrokinetic force balance”, K.T. Liao, M. Tsegaye, V. Chaurey, C.F. Chou, N. Swami*. Electrophoresis (2012), 33, 1958-1966. Journal Impact Factor =3.3; DOI: 10.1002/elps.201100707 ; Download
Nathan Swami
We describe a methodology to steeply enhance streptavidin protein pre-concentration within physiological media over that achieved through negative dielectrophoresis at nanoscale constriction gap devices, by utilizing an additional DC field offset to exponentially enhance the extent of protein depletion across the device. These protein pre-concentration methodologies may be applied towards biomarker discovery, protein crystallization, and rare target sensing for early disease diagnostics.

32. “Floating electrode enhanced constriction dielectrophoresis for trapping of nanoscale biomolecules in high-conductivity media”, V. Chaurey, C.F. Polanco, C.F. Chou, N. Swami*, Biomicrofluidics (2012) 6 (1), 012806. Journal Impact Factor = 3.5; DOI: 10.1063/1.3676069; Download
Nathan Swami
We present an electrokinetic framework for designing insulator constriction-based dielectrophoresis devices with enhanced ability to trap nanoscale biomolecules in physiological media of high conductivity, through coupling short-range dielectrophoresis forces with long-range electrothermal flow by utilizing an electrode edge to create a high field region and cause localized stirring by fluid circulation in its vicinity.

31. “Alignment and composition of laminin-polycaprolactone nanofiber blends enhance peripheral nerve regeneration”, Neal, R.; Tholpady, S.; Foley, P.; Swami, N.; Ogle, R.; Botchwey, E.*, Journal of Biomedical Materials Research: Part A (2011), 100, 406-423. Journal Impact Factor =2.6; Download

30. “Electrochemical Impedance Spectroscopy for Probing Semiconductor Surface Charge Modulation through monolayer de-protonation”, F. Camacho- Alanis, H. Castenada, G. Zangari, N. Swami*, Langmuir (2011), 27, 11273-11277. Journal Impact Factor = 4.1. Download
Nathan Swami
Modulation of semiconductor surface charge through induced dipoles and conformational changes of bound self-assembled monolayers is widely applied within sensor paradigms. Herein, modifications to the space charge region of p+ and p-GaAs due to surface charge modulation by pH-induced de-protonation of bound carboxylic acid terminal monolayers were studied by electrochemical impedance spectroscopy and correlated to flat-band potential measurements from Mott-Schottky plots. We infer that the negative surface dipole formed on GaAs due to monolayer de-protonation causes an enhancement of the downward interfacial band-bending. The space charge layer modifications were correlated to intermolecular electrostatic interactions and semiconductor depletion characteristics.

29. “Titania Nanotubes: Novel Nanostructures for Improved Osseointegration”, N. Swami, Z. Cui, L.S. Nair*, ASME J. Heat Transfer (2010), 133. Journal Impact Factor = 1.96; Download

28. “Interplay of electrical forces for alignment of sub-100 nm electrospun nanofibers at insulator gap collectors”, V. Chaurey, P. Chiang, C. Polanco, R. Su, C.F. Chou, N. Swami*. Langmuir (2010), 26 (24), pp 19022–19026. Journal Impact Factor = 4.1; Download
Nathan Swami
We present a quantitative design methodology for optimizing insulator gap width, gap resistivity and collector to needle height for the alignment of sub-100 nm electrospun nanofibers at insulator gaps of metal collectors. Enhancement of the spatial extent of alignment forces at insulator gaps, due to the concerted action of attractive stretching forces from the modified electric fields and repulsive forces from residual charges on un-discharged fibers in the gap is studied.

27. “Electrochemical impedance spectroscopy of carboxylic-acid terminal alkanethiol monolayers on GaAs of varying substrate doping”, L. Wu, F. Camacho-Alanis, H. Castenada, G. Zangari, N. Swami*, Electrochimica Acta (2010) 55, 8758–8765. Journal Impact Factor = 4.1; Download
Nathan Swami
Adsorbate-induced charge depolarization can influence the organization of self-assembled monolayers (SAMs) on semiconductor surfaces, especially as a function of the SAM functional group, SAM length and substrate dopant level and type. Based on systematic differences in the frequency response of the electrochemical impedance and phase data for carboxylic acid terminal alkanethiol layers of varying alkane chain length assembled on GaAs substrates of different dopant level and type, we assessed the relative monolayer quality to compare the proportion of defects and SAM-induced semiconductor depolarization.

26. “Photoelectrochemical Stability of Electrodeposited Cu2O Films”, Lingling Wu, Lok-kun Tsui, Nathan Swami, Giovanni Zangari*, Journal of Physical Chemistry C (2010) 114, 11551-11556. Journal Impact Factor = 4.22 Download
Nathan Swami
We report on the photoelectrochemical stability of electrodeposited films of cuprous oxide (Cu2O) in aqueous solutions, by monitoring the photocurrent within a voltage window where only the CuO/Cu2O transformation would occur. The Cu2O film morphology evolves from a dense structure to a more stable network of elongated leaf-like crystals. We attributed this behavior to the energy differences among the various crystallographic facets of Cu2O, with the {111} facets being the most stable.

25. “Enhancing DNA hybridization kinetics through constriction-based dielectrophoresis”, N. Swami*, C.F. Chou, V. Ramamurthy, V. Chaurey, Lab on a chip (2009) 9, 3212-3220. Journal Impact Factor = 5.7 Download
Nathan Swami
The enhancement of signal sensitivity through the scaling-down of sensors presents mass transport limitations that can arrest the sensitivity gains obtained as a result of miniaturization. To alleviate these limitations, we study the application of constriction-based dielectrophoresis to enhance transport through pre-concentration of target DNA in the vicinity of the diffusion layer of the sensor, on which capture probe DNA molecules were immobilized. We demonstrate that constriction-based DEP pre-concentration was not impeded by scaling-down of the sensor, as long as the sensor electrode was composed of nanostructured edges and was coupled to an equally scaled down insulating constriction within a microfluidic channel to enhance the focusing effects of the constrictions, thereby enhancing DNA hybridization kinetics at target concentration values down to the sensitivity limit of 10 pM for the sensor platform.

24. “Using Expert Elicitation to Prioritize Resource Allocation for Risk Identification for Nanosilver”, Emma Fauss, Michael E. Gorman, and Nathan Swami, J. Law Medicine & Ethics, (2009) Vol 37, Issue 4, 770-780.

23. “Moral Imagination, Trading Zones, and the Role of the Ethicist in Nanotechnology”, M. E. Gorman, P. H. Werhane, N. Swami, Nanoethics (2009), 3, 185-195.

The societal and ethical impacts of emerging technological and business systems cannot entirely be foreseen; therefore, management of these innovations will require at least some ethicists to work closely with researchers. This is particularly critical in the development of new systems because the maximum degrees of freedom for changing technological direction occurs at or just after the point of breakthrough; that is also the point where the long-term implications are hardest to visualize. Recent work on shared expertise in Science & Technology Studies (STS) can help create productive collaborations among scientists, engineers, ethicists and other stakeholders as these new systems are designed and implemented. But collaboration across these disciplines will be successful only if scientists, engineers, and ethicists can communicate meaningfully with each other. The establishment of a trading zone coupled with moral imagination present one method for such collaborative communication.

22. “Fabrication and characterization of interconnected molecular devices in a nanowell crossbar architecture”, Z. Martin, N. Majumdar, M. Cabral, F. Camacho-Alanis, N. Gergel, N. Swami*, L. Harriott, Y. Yao, J. Tour, D. Long, R. Shashidhar, IEEE Trans. Nanotechnology (2009) 8, 574-581. Journal Impact Factor = 2.0; Download
Nathan Swami
The implementation of circuit architectures based on molecular electronic devices has been impeded by the availability of facile fabrication schemes for the interconnection of individual devices. The deposition and patterning of a top contact layer between adjoining devices for interconnection purposes can result in contacts of poor fidelity, which introduces artifacts in the I-V characteristics that are not attributable to molecular transport between the contacts. In this study, through the fabrication of interconnected devices within the crossbar device architecture, we demonstrate that the vapor-phase molecular deposition method for fabrication of device layers was compatible with the massively parallel microelectronic fabrication process of liftoff, for patterning of contact layers. Based on the persistence of I-V characteristics down to 100 K, and the observation of switching between "high" and "low" conductivity states at characteristic threshold voltages at all temperatures, only with nitro-OPE molecular devices, and not with plain-OPE molecular devices, we conclude that the observed transport was a characteristic molecular signature not dependent on filament formation at contacts.

21. “Electrolytic Gold Deposition on Dodecanethiol-Modified Gold Films.” G. Pattanaik, W. Shao, N. Swami, G. Zangari*. Langmuir. (2009), 25, pp 5031–5038. Journal Impact Factor = 4.1; Download
Nathan Swami
The electrochemical nucleation and growth of Au from a sulfite electrolyte onto dodecanethiol-modified Au surfaces is investigated by a combination of microscopy and chronoamperometry methods. The self-assembled dodecanethiol monolayers are continuous but exhibit defects in correspondence of the Au grain boundaries and on top of Au terraces. Nucleation of Au films occurs initially at these defect sites, but only a small fraction of these nuclei survive an initial competition process. The remaining nuclei expand through three-dimensional progressive nucleation followed by diffusion-limited growth. Metal growth onto self-assembled monolayer-modified substrates can thus provide an alternative method for controlling film morphology for a wide range of applications.

20. “Molecular junctions of ~1 nm device length on self-assembled monolayer modified n- vs. p-GaAs”, F. Camacho-Alanis, L. Wu+, G. Zangari, N. Swami*, Journal of Materials Chemistry, 18, 5459-5467 (2008). Journal Impact Factor = 6.1; Download
Nathan Swami
Fabrication of high-fidelity molecular junctions of 1 nm or less device length is a significant challenge due to penetration of the top contact through the molecular layer. Successively smaller device lengths allow for molecules to more strongly modulate semiconductor surface charge and conductivity for device gating applications; hence, it is of great interest to better understand electron transport over device length scales of ~1 nm. In this study, the transport characteristics of molecular junctions of ~1 nm device length formed by complexation and electroless deposition (ELD) of copper on self-assembled monolayer (SAM) modified n- and p-GaAs surfaces was investigated.

19. “Identification of Risks in the Life-Cycle of Nanotechnology-Based Products”, Wardak, A.; Gorman, M. E.; Deshpande S.; Swami, N.*, Journal of Industrial Ecology, 12, 1-14 (2008). Journal Impact Factor = 2.3 Download
Nathan Swami
In order to realize the projected market potential of nanotechnology, the uncertainties to the environment, health, and safety (EHS) posed by a nano-product need to be characterized through identification of risks and opportunities in early stages of product development. We present a methodology to identify risks from nano-products using a scenario analysis approach that allows for expert elicitation on a set of preidentified use and disposal scenarios and what we have labeled “risk triggers” to obtain scores on their likelihood of occurrence and severity.

18. “THz characterization of all-trans and 9-cis retinal: experiment, and modeling”, Wright T. J. +, Luo Y., Globus T., Gelmont B., Khromova T., Swami N., Isin A. IEEE Sensors Journal (2008) 8, 781-785. Journal Impact Factor = 1.61;

17. “Terahertz (THz) electromagnetic field enhancement in periodic subwavelength structures”, Gelmont, B., Parthasarathy R., Globus T., Bykhovski A., Swami N. IEEE Sensors Journal, (2008) 8, 791-796. Journal Impact Factor = 1.61;

16. “Enhanced Coupling of Subterahertz Radiation with Semiconductor Periodic Slot Arrays”, R. Parthasarathy, A. Bykhovski, B. Gelmont, T. Globus, N. Swami, D. Woolard, Physical Review Letters 98, 153906 (2007); DOI: Journal Impact Factor = 7.18; Download
Nathan Swami
The coupling of TM polarized subterahertz (THz) radiation with periodic semiconductor rectangular slot arrays was studied, using InSb as an example. Simulation results showed that the structure with 4–12   μm thickness provides over a 20–30-fold increase in the electric field at slot edges in a nanosize region (∼500  nm). The enhancement of the THz electromagnetic field extends across the slots and reaches peak values at the edges due to discontinuity effects. Because of the strong local electromagnetic field enhancement, the structure can potentially be used for the development of novel biophotonic sensors, leading to improved detection sensitivity.

15. “The Effects of Molecular Environments on the Electrical Switching with Memory of Nitro-Containing OPEs”, N. Gergel-Hackett, N. Majumdar, Z. Martin, N. Swami, L. R. Harriott, J. C. Bean*, Gyana Pattanaik and Giovanni Zangari, Y. Zhu and L. Pu, Y. Yao and J. M. Tour, Journal of Vacuum Science & Technology A, 24 (4): 1243-1248 (2006). Journal Impact Factor = 1.40; Download

14. “Environmental Regulation of Nanotechnology and TSCA”, Wardak, A.; Gorman, M.E.; Swami, N.; Rajeski, D. IEEE Technology and Society Magazine (2007), 2, 48-56. Download

"The Product Life Cycle and Challenges to Nanotechnology Regulation", A. Wardak, N. Swami, and M. Gorman*, Nanotechnology Law & Business (2006), 3, 507-519.

13."The Product Life Cycle and Challenges to Nanotechnology Regulation", A. Wardak†, N. Swami, and M. Gorman*, Nanotechnology Law & Business (2006), 3, 507-519.

12. “Dielectric Properties of Biological Molecules in the Terahertz Gap”, Parthasarathy, R.; Globus, T*; Khromova, T; Swami, N.; Woolard, D. Applied Physics Letters (2005), 87, 113901-113903. Journal Impact Factor = 3.72, Download
Nathan Swami
Results from parallel measurements of reflection and transmission spectra of biological molecules were utilized to enable detailed and direct calculation of the refractive index and absorption coefficient spectra in the Terahertz gap. The DNA samples from herring and salmon, as well as the protein Ovalbumin sample, have been characterized. The reflection spectra have resonance features similar to those demonstrated earlier for transmission, thereby reaffirming molecular vibrational modes in biological materials. The dispersion of refractive index and absorption coefficient is demonstrated within the Terahertz gap of 10 cm−1 to 25 cm−1.

11. “Two-potential electrochemical probe for study of DNA immobilization”, N. Swami*, C.F. Chou, R. Terbrueggen, Langmuir (2005) 21, 1937-1941. Journal Impact Factor = 4.1, Download
Nathan Swami
A two-potential electrochemical method based on the first and fourth harmonic signal is applied to study DNA immobilization, by the simultaneous characterization of capture probe DNA self-assembled monolayers and hybridized target DNA molecules on a gold electrode surface. Capture probe and target DNA strands are labeled with ferrocenes composed of differing chemical environments, to permit their simultaneous, yet independent signaling at different formal potentials, so that their respective signals may be de-convoluted and assessed for relative surface concentration.

10. “Room Temperature Molecular Memory Observed from a Nanowell Device”, N. Gergel, N. Majumdar, N. Swami, L. R. Harriott, J. C. Bean, J. M. Tour, J. Vac. Sci. Tech. A (2005), 23 (4): 880-885. Journal Impact Factor = 1.40; Download
Nathan Swami
We tested the electrical characteristics of an oligo(phenylene ethynylene) (OPE) molecule with one nitro side group, an OPE with two nitro side groups, and an OPE with no nitro side groups in a nanowell device. The OPE molecule with nitro side group(s) showed switching behavior with memory as well as nonreversible negative differential resistance (NDR). Current-voltage (I‐V) characteristics showed a high conductivity state that switched to a low conductivity state upon the application of a threshold voltage. This low state held until the opposite threshold voltage was applied and the device switched back to the high conductivity state. The OPE with no nitro side groups did not show memory or NDR.

9. “A miniaturized cyclic PCR device - modeling and experiments”, C.F. Chou, R. Changrani, P. Roberts, D. Sadler, J. Burdon, F. Zenhausern, S. Lin, A. Mulholland, N. Swami, R. Terbrueggen, Microelectronic Engineering, (2002) 61-2: 921-925. Journal Impact Factor = 1.57, Download

8. “Electrical properties of K-doped superfulleride thin films”, N. Swami x, M.E. Thompson, B.E. Koel*, Journal of Applied Physics (1999), 85, 3696. Journal Impact Factor = 2.21, Download

7. “Polymerization and decomposition of C60 on Pt(111) surfaces”, N. Swami x, H. He, B.E. Koel*, Physical Review B (1999), 59 (12), 8283–8291. Journal Impact Factor = 3.07, Download

6. “Control of the growth of ordered C60 films by chemical modifications of Pt(111) surfaces”, H. He, N. Swami x, B.E. Koel*, Thin Solid Films (1999), 348, 30-37. Journal Impact Factor = 1.94, Download

5. “Reaction of C60 with oxygen adatoms on Pt(111)”, H. He, N. Swami x, B.E. Koel*, Journal of Chemical Physics (1999) 110 (2). Journal Impact Factor = 3.15, Download

4. “Ordering and stabilization of C60 films on the Sn/Pt(111) surface alloy”, N. Swami x, H. He, B.E. Koel*, Surface Science, 425 (1999) 141-151. Journal Impact Factor = 1.78, Download

3. “Growth and characterization of potassium-doped superfulleride thin films”, N. Swami x, Y. You, M. Thompson, B. Koel*, Journal of Vacuum Science and Technology A (1998), 16 (4). Journal Impact Factor = 1.40, Download

2. “Probing the structures of bimetallic Sn/Rh(111) surfaces”, Y. Li, M. Voss, N. Swami x, Y. Tsai, B.E. Koel*, Physical Review B (1997), 56 (24). Journal Impact Factor = 3.07, Download

1. “Kinetics of zinc removal from cobalt electrolytes by ion exchange”, N. Swami x, D.B. Dreisinger*, Solvent Extraction and Ion Exchange (1995) 13 (6) 1037. Journal Impact Factor = 1.29, Download

Peer-Reviewed Book Chapters

2. "Case Study of an Emergent Nanotechnology: Identifying environmental risks from silver nanotechnology through an expert elicitation methodology".Fauss, E., Gorman, M.E., Swami N. ACS Book Title: Biotechnology and Nanotechnology Risk Assessment; bk-2010-00432d.

1. “A Framework for using Nanotechnology to Improve Water Quality.” Gorman, M. E., Wardak, A., Fauss, E., and Swami, N. Nanotechnology Applications for Clean Water. Edited by Savage, N., Diallo, M., Duncan, J., Street, A., and Sustich, R. New York: William Andrew Inc., 2009. Download NNI Grand Challenge Workshop Report: “Regional, State, and Local Initiatives in Nanotechnology”, S. Murdock, B. Stein, S. Crosby, N. Swami, NNI Workshop Report, National Science and Technology Council Committee on Technology; Subcommittee on Nanoscale Science, Engineering, and Technology. Download

“Interactions of C60 with the Pt(111) surface, adatoms and surface alloys”, N. Swami x, H. He, B.E. Koel*, Platinum Metals Review, 43 (3) Jul 99 p.129.