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The presence of outliers deteriorates the overall performance of an electronic nose and, thus their detection and removal is critical to achieve the optimum discrimination ability among the subjected volatile organic compounds/gases. This article reports a semi supervised fuzzy ${c}$ -means clustering based outlier detection method in the context of an electronic nose. A novel threshold criterion is developed using the fuzzy membership values and is used to evaluate whether the electronic nose response is an outlier or a true data sample. The method is tested on two experimentally generated electronic nose datasets using different types of sensor arrays. As the experimental datasets does not contain outliers, a mathematical outlier generation model is developed for outlier generation following the inherent properties of outliers. The proposed method effectively discriminates among the true data samples and the outliers for both the electronic nose datasets.

Dual gate field-effect transistors (DGISFETs) have prompted interest because of the sensitivities higher than the Nernst limit through capacitive coupling. The bottom gate (BG)–semiconductor interf...

Multi Verse Optimization (MVO) technique is a newly developed population based algorithm established on the perception of white holes and black holes in a multi-verse for finding out all possibilit...

The role of 3-dimensional (3-D) geometries in facilitating surface reactions in microchannels is the subject of the present work. 3-D microfluidic immunosensor geometries inspired from the design of packed bed columns, utilizing splitting and recombination of flows in improving the transport in flow heterogeneous microfluidic immunosensors, were studied systematically. First, the effect of the passive mixing on the antigen capture was tested experimentally using prostate specific antigen (PSA) and anti-PSA and validated using numerical studies. Subsequently, numerical studies on the effects of geometrical parameters like the height and width of the microchannel, the height and width of the grooves, number of groove sets, the ratio of the heights of the grooves and the microchannel etc., on the antigen capture were conducted. The Sherwood number (Sh) and Peclet number (Pe) were used to explain the mass transfer. Finally, the optimum Peclet number (Pe∼x223C 3400) was found, having a maximum figure of merit ratio for the grooved to the ungrooved microchannels Correlations were also obtained between the average surface concentration and the geometrical parameters. The paper presents novel scientific results which are useful for designing efficient heterogeneous immunosensors.

Metal oxide-Polyaniline (PANI) nanocomposites have shown improved gas sensing characteristics that can be attributed to the formation of a p–n junction between the n-type metal oxide and the p-type PANI. The charge transport, grain boundary depletion region, and intragrain resistance are studied to understand the gas sensing mechanism of pristine metal oxide gas sensors. However, gas sensing mechanisms for metal-oxide/PANI nanocomposites have not been studied extensively. In this work, we have studied the gas sensing mechanism of SnO2/PANI nanocomposites using electrochemical impedance spectroscopy, and temperature dependent gas sensing experiments. Well-defined SnO2 nanoclusters were observed in the PANI matrix. The n-type SnO2 was covered by p-type PANI, and a depletion region was formed at the interface. The presence of the p–n junction depletion region was confirmed by impedance spectroscopy. The polarons in PANI were trapped by NH3 leading to a change in the width of the conducting path due to rearrangement of charge carriers along the depletion region. The change in the conduction path, along with the trapped polarons, enhanced the sensor response. For higher loadings of SnO2, the depletion region was deformed, and the sensor response decreased due to non-uniform boundaries. 1 wt% SnO2 with respect to aniline precursor in in situ synthesis showed the best response of 37.8% for 100 ppm NH3 at 35 °C. The response was stable for low humidity levels up to 51%RH. The response increased for higher humidity levels. The sensor response increased from 0.17 to 2.99 upon bending 1000 times at 7.8 mm diameter due to cracks in the surface. The sensor showed only 10% variation in response after 9 months.

Hafnium oxide films have elicited interest in the field-effect transistors because of the high dielectric constant, high band gap and the good interface with oxide semiconductors. In this work, sputtered deposition and post-annealing of hafnium oxide films were studied for reduction of defects at the surface of gate dielectric. AFM and FTIR characterization of the films were conducted. A Metal-Insulator-Metal device was demonstrated for the identification of the capacitance of gate dielectric. The effect of the material properties on the performance of field -effect transistors were investigated.

Dual gate ion sensitive field effect transistors (DGISFETs) have elicited interest due to the capability to provide pH sensitivity values several times the Nernst limit. The interfaces in the devic...

In a typical heterogeneous microfluidic immunosensor, the carrier fluid transports the target analytes to the antibodies immobilized on the channel surfaces with a thin liquid layer where they are captured. While single-phase systems (the carrier fluid being a liquid) are well studied, two-phase systems (the carrier fluid being a gas) are less explored. There in particular, the effect of transport parameters on the capture efficiency (a critical performance parameter) has not received much attention, and thus is the subject of study here. Hence, we have investigated the transport and capture of analytes in a two-phase heterogeneous microfluidic immunosensor wherein the target analytes in the gaseous phase are transported to the immobilized antibodies via gas–liquid interfacial mass transfer which strongly depends on flow variables of the gas phase flow. Parametric studies on capture efficiency using the properties of trinitrotoluene (TNT) were used to obtain the effects of important transport parameters on the capture of analyte molecules. The highlight of this work is the development of an empirical correlation between the capture efficiency and the gas-side non-dimensional interfacial mass transfer coefficient (Sherwood number, Shg). This could help design of a two-phase microfluidic device with improved performance parameters to capture gaseous analytes.

The enhanced capture of the antigen (Ag) by the surface-immobilized antibodies (Ab) in heterogeneous microfluidic immunosensors lowers (improves) the detection limit thus facilitating the early disease detection. The efficient capture of the antigen is subjected to the interaction of the transport parameters, reaction parameters and the microfluidic system geometry. In the present work, the role of active mixing in facilitating the transport in flow-based heterogeneous immunosensor was studied, both numerically and experimentally. The experiments were performed with the capture of prostate-specific antigen (PSA) by anti-PSA and the results were validated using numerical simulations. The average Sherwood number (Sh) for the experiments and simulations was comparable. First, the effect of the nature of the flow on the capture efficiency was tested, which showed the enhancement in the antigen capture using active mixing. Further, studies of individual active mixing parameter (average velocity, frequency and amplitude) on analyte capture were conducted. The increase in average velocity (uavg) increases the antigen capture but the corresponding pressure drop also increases, and the figure of merit (FOM) attains a maximum at Re ~ 0.6. Similar behavior was observed with the increase of the frequency. The continuous increase in the frequency reduces the reaction time scale and decreases the analyte capture. The amplitude has the least effect on the antigen capture. The flow profiles were also seen and the temporal variation was compared at different flow conditions with micro-PIV. We also proposed two correlations utilizing the parameters—the average surface concentration (Cs,avg), the Reynolds number (Re) and the Strouhal number (St). The correlations indicate that the dependency coefficient for St is higher than Re, and signify the impact of vortex propagation (i.e., active mixing) on antigen capture.

The evaporation of antigen-laden sessile droplets on antibody-immobilized PDMS substrates could be used in place of microwells for detection purposes owing to the lesser requirements of analytes and a reduced reaction time. To develop such techniques, the effects of different parameters on the reaction efficiency and on the resulting deposition patterns of antigens on the surface after evaporation need to be well understood. While the resultant deposition patterns from the evaporation of droplets of biological fluids on surfaces are being studied for various biomedical applications, systems where the analyte of interest in the droplet binds to the surface have not been investigated until now. While the effect of temperature on the internal convection within sessile droplets has been studied, the effect of the analyte (antigen in this work) concentration and the analyte-surface (antigen-antibody in this work) binding on the internal convection has not been studied until now. Therefore, to gain insight, the evaporation dynamics of sessile droplets with different concentrations of antigens along with polystyrene microspheres (used as tracers) in phosphate-buffered saline (PBS) on antibody-immobilized PDMS substrates were experimentally studied using microparticle image velocimetry (PIV). It was found that Marangoni flow due to concentration gradients and surface reactions was responsible for the observed velocity field. The antibody-antigen reaction (as compared to the control case of no surface reaction) and higher concentrations of prostate specific antigen (PSA) resulted in increased strength of Marangoni convection. To obtain further insight into the different deposition patterns obtained, the contributions of different particle-particle and particle-substrate forces were determined, and it was observed that the Marangoni forces along with surface tension and DLVO forces create a uniform deposition of the particles present within the droplet. This learning could be used to design biosensors.

Electronic nose is a chemical sensor array-based chemical identification system for chemical analyte recognition and quantification. Regarding chemical analyte recognition methods, plenty of work is reported in the literature but relatively less attention is paid towards the quantification techniques. PLS regression is a well-known quantification technique. This work presents a fuzzy c-means clustering-based uncertainty measure computed by using the concept of Shannon entropy, for the data sample weighting, which enhances the quantification efficiency of PLS regression technique. The method is validated on the three electronic nose data sets available from the published literature.

SAW sensor is a well-known chemical sensor used for the identification of different chemical vapors. When a vapor is subjected to the SAW sensor, it results a unique dynamic trace as a transient signal which encodes its identity information. By analyzing this transient signal, the identity of the vapors can be obtained. This work presents an improved wavelet-assisted phase space-based vapor identification methodology for SAW sensor analysis. The phase space is created by computing the transient signal and its first time derivative. The performance of the proposed approach is compared with commonly used wavelet-assisted transient signal analysis in the measurement space. The discrimination analysis is performed qualitatively by principal component analysis and quantitatively by class separability measure. In this work, seven organic vapors are subjected to a PIB-coated SAW sensor in virtual environment and their transient responses are simulated. For making the transient responses near to the actual experimental conditions, random noise is added into the responses. It is observed that the wavelet-assisted phase space analysis shows better discrimination in principal component space and produces more than four times separability in comparison to the wavelet-assisted transient signal analysis.

The chemical sensor array is a key unit of electronic noses and polymers are popular choices as the sensing materials. The selection of the polymers is an important aspect in designing the array. While the conventional approach for polymer selection which is based on the analysis of a large sensor array response (SAR) in smaller subsets of arrays is very well explored, relatively less attention has been given to another approach which is based on the LSER parameters of the polymers and the analytes. Although both of these approaches of polymer selection have independently shown to select the efficient subset of polymers, however the efficiency of the LSER parameters based approach has not yet been benchmarked with the conventional sensor array response approach. And this is the motivation of our work. In this paper we present a comparative analysis of these two approaches using the principal component analysis in combination with raw as well as standardized data, as a common method of polymer selection utilizing two SAW chemical sensor array response data sets available from the published literature. The study shows that the optimum sets of polymers are obtained with the raw noise-free SAR data but not with either the raw noisy data or the standardized (both noise-free/noisy) data. The same optimum sets are also obtained by the raw LSER parameters based approach which can be used as it is difficult to generate completely noise-free SAR data. The significance of this work is that the conditions when the results of the simpler LSER based approach would match those of the elaborate SAR based approach for the data sets chosen are provided. We believe that this detailed work, not reported earlier, will advances the scientific knowledge in the field and help to facilitate the design of the sensor arrays.

Cu-phthalocyanine (CuPc) and five of its metal variants (M = Mg, Mn, Co, Ni, and Zn) have been studied by density functional theory (DFT) methods for sensing five volatile organic compounds – isoprene, acetone, ammonia, methanol, and methane. Having performed experimental validation of the methods, interaction energies, binding configurations, changes in charge distributions and energy levels after interaction, and interaction barriers were studied to account for the sensitivity trend across the analytes for CuPc, while also providing supporting data from experiments carried out herein. It is also demonstrated that relatively simple calculations of interaction barrier can result in quick screening of metal-Pc variants for an analyte without any extensive experimental or computational efforts. Present literature lacks such detailed studies for these materials and analytes. Thus, this work would consolidate the understanding of sensing phenomena at the electronic structure level that could be useful for emerging technologies in gas sensing.

In heterogeneous microfluidic immunosensors, enhanced capture efficiencies of the antigens (Ag) in the carrier fluids by the surface-immobilized antibodies (Ab) facilitate lower detection limits and thus early detection of disease. Capture efficiency depends on the interplay of transport, reaction parameters and the geometry of the system. A detailed analysis on the enhanced capture efficiencies due to secondary flows in heterogeneous immunosensors has not received significant attention and is the theme of the present work. We conducted a systematic study to observe the significance of secondary forces on the capture efficiency, manifested as the average surface concentration (Cs,avg), in serpentine channels of different lengths (l) and radius of curvature (Rc) as a function of the Reynolds number (Re). Experimental observations were validated with numerical simulations. Micro-PIV studies at different planes and sections of the serpentine microchannels were conducted and matched with the simulated velocity profiles. Further investigation of the process and the geometrical parameters was conducted using numerical simulation and the behaviour of Cs,avg as a function of Re and Rc was plotted for different cases. A highlight of the present work are correlations of Cs,avg as a function of the Dean number (De), as well as its constituents (Re and α). The scientific studies of the geometrical and process parameters which affect the analyte capture advance the understanding of the phenomena and the proposed engineering correlations would be useful in the design of more efficient flow-based heterogeneous immunosensors.

Although that the continuous tunability of InGaN/GaN QW LEDs, carries the promise of a significant impact in optoelectronics, the reduction of the square of the overlap of electron and hole wave functions ( M e h 2 ) in InGaN/GaN QW LEDs, under certain conditions, is a sizable problem, difficult to overcome. Theoretical investigations have been carried out on the incorporation of Indium (In) in the GaN barrier layers, with an aim of increasing the overlap of electron and hole wave functions. Rigorous studies through the self consistent solution of Schrodinger and Poison equations expose some new and striking results. With suitable doping, the inclusion of In in the barriers can increase M e h 2 to more than two times that of a conventional InGaN/GaN QW LED. In in the barrier along with doping may be suitably utilized to tailor the transition energy and M e h 2 with current density, as desired. The transition energy and the M e h 2 may be made to have a positive or a negative slope with current density or they may be made fairly constant. This paper will outline the theoretical details, computational methodologies, the parameters used, and the striking new results with suitable depictions and discussions. These new information ought to be interesting for current optoelectronics.

A polyaniline copolymer derivative with iminodiacetic acid synthesized in a recent work (Dutta et al., 2018) had shown selectivity to cadmium ion and the interference behaviour with heavy metal ions studied using the concepts of mass transport, charge transport and thermodynamics, were divided into four classes. The motivation for the present work, is to understand the molecular level interaction of the same copolymer derivative with heavy metal ions belonging to these four classes using density functional theory (DFT). In this work, a molecular model of polyaniline copolymer derivative with iminodiacetic acid is developed. The interference behavior of the polymer with metal ions belonging to each of the four classes is investigated through calculation of binding energy, stability constant and charge transfer between polyaniline copolymer and metal ion. The simulation results were in good agreement with the experimentally observed phenomena indicating that the polymer is selective to cadmium.

Spectral properties of dyes change upon attachment to surfaces which need to be understood. While the effects of surface properties affecting the changes such as Bronsted acidity is well-covered, that of surface energy components is not well studied. In this work, two dyes with different number of carboxylic groups were attached on three surfaces (PET, PDMS, and silicon). It was observed the “surface energy components” rather than “total surface free energy” were more pertinent in explaining changes in the spectral properties of the immobilized dyes. An increase in the basic component of surface energy favored monomer formation, while a decrease favored agglomeration. Thus, tuning the spectra of a dye by using surfaces with different surface energy components enables use of the dye for different applications. As an application, dye attached on PET substrate showed promise as optical pH sensor in the range of pH 7–10.

Shift of the emission spectrum and the efficiency loss with the operating current are the major challenges in the conventional InGaN/GaN QW LEDs. Several approaches are being tried by different research groups to overcome this hurdle, including, introduction of In in the barriers for which a rigorous study seemed essential. In this paper, our comprehensive and systematic studies on InGaN/InGaN quantum well light emitting diodes reveal that the overlap of electron and hole wave functions can be increased even at low operating currents by the introduction of In in the barriers. The changes of output emission for different In content in the barrier and various doping at different currents are reported, which show that the shift of the energy can be minimized for suitable choice of parameters. The emission and the overlap of electron and hole wave functions have a significant dependence on the doping in the barrier layers which may be used advantageously. Computations have been performed through the self-consistent solutions of Schrodinger and Poisson equations.

Organic dyes, both in solution phase and in immobilized condition, are useful tools for optical detection. Studies have shown that spectral property of dyes in solution are different from that in the immobilized state. In this work, we have studied the optical properties of dyes in solution as well as in immobilized state with three categories of dyes, mono-carboxylic mono-functional, bi-carboxylic bi functional and bi-carboxylic mono-functional. Two linkers (APTES and PEI) were used for attaching the dyes to the silanol terminated silicon surface. Geometries were optimized using density functional theory. Time dependant density functional theory was used to calculate the absorption spectra of free and attached dyes. B3LYP and CAM-B3LYP hybrid functional were used for the theoretical calculations. Experimental results showed that dyes upon immobilization experienced a large red shift in the absorption maxima. The value of the red shift in absorption maxima was comparable for both the linkers. Theoretical calculations indicated this large shift is not due to bond formation between dye and the linker. This leads to the conclusion that aggregation takes place between dye molecules upon immobilization but not in solution, and this causes the large red shift in the absorption maxima values of the immobilized dyes.

A dual-gate amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistor (TFT) was studied to obtain a pH sensitivity of $\sim 160$ mV/pH, which is above Nernst limit (59 mV/pH) with a low value of operating voltage (−5 to 5 V). The utilization of the active layer itself as the sensitive surface constitutes the dual-gate TFT structure with the back-channel gated with the electrolyte. The TFT characteristics were optimized by annealing the IGZO film in varying temperatures in oxygen ambience. A double-layered a-IGZO was used to sandwich the source/drain electrodes to eliminate the issues related with the high contact resistance and critical passivation of source/drain electrodes to protect from the exposure of the electrolyte. The single-gate electrolyte-gated thin film transistor showed the pH sensitivity of 24 mV/pH, which was enhanced by 6.7-fold by its dual-gate operation. The operation of dual-gate TFT ion-sensitive field-effect transistors (ISFETs) with varying only bottom gate voltage eliminates the requirement of a reference electrode necessary in single-gate ISFETs. Such dual-gate ISFETs obviate the need of an additional high- $K$ dielectric needed for the dual-gate TFT ISFETs and could also be fabricated on flexible substrates. These structures with the high sensitivity of $\sim 160$ mV/pH and requiring low ( $\sim 2~\mu \text{L}$ ) analyte solution could be the potential candidates for utilization as chemical and bio-sensors.

The emission spectrum of the conventional InGaN/GaN quantum well (QW) diode changes remarkably with the operating current. The degree of change depends on the constituent parameters of the QW. A detailed investigation has been carried out through the self-consistent solutions of the Schrodinger and Poisson equations to elucidate the change of the emission energy and the transition probability with the operating current and to explore how the changes depend on the well width of the QW and the In mole fraction. It is found that choosing suitable values of the mentioned parameters, the emission energy may be kept almost constant with current, or it may be tuned over a wide range through current. The two possibilities have immense importance for optoelectronic device applications.

Nanoscale films having thicknesses in the range of 92 nm–137 nm were obtained by spin coating V 2 O 5 sol at different stages of aging. The observed structural and morphological changes with time can be attributed to the reactions occurring in the sol. The film morphology changed from an indistinctive featureless film to a homogenous film having ribbon-like nanostructures with aging of sols. TGA and FTIR analysis confirmed loss in the amount of intercalated water content with aging giving rise to structural changes (decrease in interlayer spacing) which were observed using XRD. Variations in mechanical, electrical, and optical properties of the thin films were observed with aging of the sol. Strain in the films were found to decrease with aging. The electrical conductivity increased with aging and this can be correlated to the improved crystallinity of the films with aging. The optical bandgap (calculated from UV–Vis data) decreased and the transmittance increased with aging.

This paper reports the use of branched polyethylenimine (BPEI) coated amorphous indium gallium zinc oxide (a-IGZO) based electrolyte gated thin film transistors (EGTFTs) to obtain a pH sensitivity of ∼110 mV pH−1 which is above the Nernst limit. The a-IGZO, used both as the active layer and pH sensitive layer, obviates the need of a separate high-K dielectric thereby simplifying the process of fabrication of TFT based sensors along with their operation at a low voltage range (−2 V to 2 V). Two EGTFT devices, one with bare a-IGZO and the other with BPEI coated a-IGZO were utilized in this work. The electrical double layer (EDL) formation at the a-IGZO/electrolyte interface was studied with the capacitance–voltage analysis which showed well defined accumulation and depletion regimes at a small voltage range (−1 V to 1 V) with the EDL capacitance of ∼2.0 μF cm−2. The EGTFT with bare a-IGZO film showed a good ION/IOFF ratio of the order of ∼103, a sub-threshold swing of 238 mV dec−1, and saturation mobility of 3.0 cm2 V−1 s−1 but a pH sensitivity of 24 mV pH−1. The utilization of BPEI with this structure, reported for the first time, resulted in ∼4.6 fold enhancement in the sensitivity. The BPEI layer enhances the pH sensitivity and could also facilitate the use of such devices for biosensing as the amine groups of the BPEI could be used as linkers for immobilizing biomolecules for capturing target analytes. The device structure used in the work is compatible for fabrication on flexible substrates which enable lower cost and applications needing form factor.

An a-IGZO based dual gate ion sensitive field effect transistor (DG ISFET) was fabricated utilizing a simple and cost effective method. Sputtered Al2O3 was used as the top gate dielectric to obtain a greater surface site density and thus a higher sensitivity due to higher surface roughness. Deteriorated characteristics of the bottom gate thin film transistor (BG TFT) caused by deposition of Al2O3, attributed to the induced oxygen vacancies at the Al2O3/a-IGZO interface were recovered by optimized annealing at 350 °C in presence of oxygen. The increased value of the OFF current (~nA) in the BG TFT upon exposure to the electrolyte (pH-4), was attributed to the formation of double channels in the active (a-IGZO) layer. The conduction in the channel formed at the Al2O3/a-IGZO interface dominated over the bottom gate channel (a-IGZO/SiO2 interface) in the turn OFF region while being comparable in the turn ON region. The fabricated DG ISFET showed ~6-fold enhancement in pH sensitivity (347.6 mV/pH) from the Nernst's limit (59 mV/pH). To validate the experimental findings, a T-CAD based simulation model was proposed by incorporating three dielectric layers to represent the electric double layer formed at the electrolyte/insulator interface and at the reference electrode.

Detection of minute quantities of target antigens in serum samples (consisting of a mixture of proteins/biomolecules) can be achieved by enhancement of the capture efficiencies of heterogeneous immunosensors. An important process parameter which affects the capture of target analytes in such immunosensors is the pH of the solution as the target proteins present in the serum samples are charged molecules. Here, we investigated the capture of prostate-specific antigens (PSAs), first in a mixed-analyte system wherein the solution contained two other non-specific proteins along with the target analyte, using the surface plasmon resonance spectroscopy. There are no reports on the detection of antigens in a mixed system based on the optimization of the pH values of the carrier fluid, and this is the motivation of the present work. Further, we studied interference effects caused by the presence of these non-specific proteins in the mixed-analyte systems by artificially increasing the ratio of the interfering proteins to that of the target protein. Eventually PSA spiked into the rabbit serum samples was captured through the optimization of the pH of the solution. We could detect PSA in the serum samples when diluted to 100 times or more, where the amounts of other interfering proteins were ~ 66 times that of the amount of PSA. This study proposes a heterogeneous immunosensor to detect the target analytes in the diluted serum samples by tuning pH the of solution mixture, which can be utilized to detect disease biomarkers in serum samples.

The possible mechanisms governing the enhancement of sensitivities of Electrolyte-insulator-semiconductor (EIS) devices upon surface modification (texturing) realized by electrostatic attachment of silica particles using 3-aminopropyl triethoxysilane (APTES) as a linker are presented. EIS devices were fabricated with a textured dielectric surface using SiO2 particles (of diameters 475, 135, and 70 nm) and screen printed Ag/AgCl electrodes. A maximum pH sensitivity of 52.4 mV/pH was achieved for the EIS device textured with 70 nm particle size while the sensitivity with the planar dielectric was 37.1 mV/pH. The APTES modification enhanced the adsorption of H + ions by protonation of the ‐NH2 to ‐NH3 + sites as seen from the capacitance versus voltage (C-V) hysteresis voltages. UV-Vis absorption and photoluminescence (PL) spectra indicated that the surface defects on the textured surface increased with decreasing particle size. Zeta potential measurements suggested a combined acid-base behavior of textured surface with the formation of ‐NH3 + and −Si-O − groups. Theflatband voltage study showed that surface textured with 70 nm SiO2 particles provided the optimum ratio of Si-OH and ‐NH2 groups. The various chemical treatments during texturization did not affect the

Higher capture efficiencies with faster response times are important performance benchmarks for heterogeneous immunosensors which are utilized in recognitions of analytes for disease detection. As the capture involves transport of antigens from the bulk solution to the surface immobilized antibodies and the subsequent binding, the transport and reaction parameters play a critical role. While there are reports on the effect of individual process parameters (temperature, extent of mixing, pH) on the antigen/antibody interaction, we are not aware of any studies on the combined effect of these process parameters, and moreover, there are limited studies on the effect of these process parameters on the reaction and transport parameters. Knowledge of the effect of the process parameters on the transport and reaction parameters is necessary to understand their relative contributions to and the mechanism involved in the capture of the antigens. In this work, we have made an attempt to quantify the transport and reaction parameters and studied their dependencies on the process parameters. Experiments were conducted with three systems – BSA/anti-BSA, PSA/anti-PSA and CRP/anti-CRP, to quantify the captured antigen. The dependencies of the process parameters on the transport and reaction parameters were obtained from the experimental data using a diffusion–convection–electromigration–reaction model. Utilizing these dependency functions, the process parameters were modeled to find the optimal conditions for the highest capture efficiencies. Specifically, the influence of pH on maximizing the antigen capture and the underlying mechanism of the electrostatic interactions based on the surface charges and zeta potentials were elucidated.

Higher capture efficiency in heterogeneous immunosensors is desirable for the detection of cancer biomarkers at low concentrations. The process of the capture of these antigens is transport limited since the rates of antigen/antibody reactions are faster. In the case of non-flow systems, diffusive transport has contributions from both translational and rotational phenomena. Since the contribution of the rotational diffusivity is comparatively less explored in the literature, we have studied the same for three antigens – bovine serum albumin (BSA), prostate specific antigen (PSA) and C-reactive proteins (CRP). We quantified the rotational diffusivities using the time resolved fluorescence anisotropy method, and further quantified the contribution of the rotational diffusivities to the overall diffusivity of the antigens, and also studied the effect of the process parameters – temperature and pH of the solution. With an increase in temperature, the rotational diffusivity increased showing Arrhenius dependence while with the variation of pH, it showed a non-monotonic behavior having maxima closer to the isoelectric point of the corresponding antigens. This interesting behavior of the pH values could be attributed to lesser electro-viscous effects when the antigen molecule is neutral around its isoelectric point. The optimization of the pH and temperature for the immunosensors could be utilized to design efficient immunosensors.

Lattice strain has immense effect on the optoelectronic properties of III–V semiconductor quantum wells (QWs), since it introduces a pronounced change on the band properties of QWs and it is often purposefully introduced to improve device performance. In this paper we report the results of our experimental and theoretical studies on, how the important parameter, the band offset, changes with strain for InxGa1−xN/GaN, GaAs/InxGa1−xP and InxGa1−xAs/AlGaAs QWs. Experimentally the band offsets have been studied through capacitance transient measurements in the form of deep level transient spectroscopy (DLTS) on suitable QWs within a Schottky diode. The energy levels in a QW are considered to be analogous to a deep trap in the forbidden energy gap. From detailed balance between the emission and capture, Arrhenius type expressions were derived to analyze transient emission data, from which the band offsets were computed. Theoretically the band positions at the heterointerfaces have been calculated from the equations developed, which directly correlate the position of the bands with the strain at the interface. The strain is calculated from the In mole fractions and lattice constants. The parameters implicitly involved are the elastic stiffness constants (C11 and C12), the hydrostatic deformation potential of the conduction band (a′), the hydrostatic deformation potential (a) and the shear deformation potential (b) for the valance band. The results should be useful to research workers in the field of optoelectronics.

There is an interest in microfluidic devices for disease detection. In microfluidic immunosensors, the microchannel surfaces are functionalized with a stack of intermediate linker molecules to the specific antibodies. The efficiency of these immunosensors depends on the effective capture of antigens flowing in the carrier fluid by the surface-immobilized antibodies. The diffusion of these antigens to these antibody-immobilized surfaces is governed by the velocity profile, which in turn is governed by the interaction of the carrier fluid molecules with the surface antibodies. We report a systematic study to characterize fluid flow of different polar liquids (water, methanol and isopropyl alcohol) in trapezoidal Si microchannels, of about 100 μm hydraulic diameter, functionalized with intermediate molecular layers along with three different antibodies immobilized via these molecular layers. The friction constants were calculated from the pressure drop measurements. We attempted to understand the solid–liquid interactions in terms of the friction constants as a function of the solid surface free energies of the terminal antibody layers (which are affected by the energetics of the underlying layers) immobilized on to the microchannels, and the polarities of the liquids flowing through these microchannels. Correlations of liquid polarities with the friction constants were seen for almost all the functionalized surfaces. A reasonable correlation of the surface energies with the friction constants was seen for most of the surfaces studied. Possible reasons for the behaviors are discussed. The measured friction constants and the knowledge of the solid–liquid interactions could facilitate improved designs of microfluidic immunosensors.

The carrier distributions, obtained from capacitance–voltage measurements on semiconductor heterojunctions, are widely different, depending on whether the Schottky barrier is on the higher band gap semiconductor or on the lower band gap semiconductor. The actual carrier distributions as calculated in both cases are quite dissimilar from the measured distributions. Explanations for such observations have been sought through rigorous studies based on self-consistent solutions of Schrodinger and Poisson equations applied to the widely used GaAs/AlGaAs heterojunctions. It emerges that the nature of the carrier distributions is mostly dependent on the effects of the Debye smearing on the two dimensional and three dimensional components of the capacitances at the heterostructures. The applied electric field, necessary for measurements does not have a significant effect on the carrier distribution.

The effects of the doping level and the operating current on the transition energy of InGaN/GaN QW diodes have been studied through the self-consistent solution of the Schrodinger and Poisson equations. Broad change in the transition energy is observed due to the doping variation. With increase in the current density the emission peak shifts toward higher energy. This shift, which is a major disadvantage of the lighting devices, is reduced significantly by increasing the doping concentration.

Enhanced antigen–antibody interactions in microfluidic immunosensors can be effected by tailoring the surface free energies of the antibody immobilized surfaces to obtain the appropriate fluid–wall interactions. We report a systematic study to evaluate the surface free energies from contact angle measurements, using the LWAB method, of different antibody (anti-BSA, anti-PSA, and anti-CRP) surfaces, each immobilized separately on to non- and nanotextured Si surfaces via a stack of functionalized layers including aminosilanes of which three different types were used. The apolar surface free energy components were independent of the physical modification in the non-functionalized and the intermediate hydrolyzed surfaces where as they depended on the nature of the surface and the chemical modifications in the subsequent functionalized stages. Surface free energies of the different antibodies immobilized with the shorter chain length aminosilane (APTES) on non- and nanotextured surfaces were in the order of anti-BSA

Capture of higher amount of antigen with higher efficiency by the antibodies in a minimum time is desired for enhanced performance of immunosensors. In this manuscript we report a systematic investigation of the effects of the nature of the silicon surfaces (whether nanotextured or not) on which antibodies are immobilized and the nature of the surface stacks in combination with the state of mixing of the solution (whether mixed or not) containing the antigens, on the kinetics of the antigen–antibody binding in a non-flow system. An important finding here is that the combination of nanotextured surfaces with the mixing of the analyte solution resulted in a higher antigen capture, higher efficiency of capture and a lower process time, compared to other combinations. Computer simulations using a transport-reaction model were used to extract the transport and reaction parameters from the experimental data. Analysis of these parameters (the maximum available antibodies on the surface per unit area, diffusivity, boundary layer thickness, the dissociation constant) helped to provide an understanding of the experimental results and thus the phenomena involved. Applications of this study include improving the sensitivity and response time of immunosensors in both non-flow and flowing systems.