Samit Gupta

Detection of clinically relevant levels of protein analyte under physiologic buffer using planar field effect transistors

Electrochemical detection of protein binding at physiological salt concentration by planar field effect transistor platforms has yet to be documented convincingly. Here we report detection of streptavidin and clinically relevant levels of biotinylated monokine induced by interferon gamma (MIG) at physiological salt concentrations with AlGaN heterojunction field effect transistors (HFETs). The AlGaN HFETs are functionalized with a silane linker and analyte-specific affinity elements. Polarity of sensor responses is as expected from n-type HFETs to negatively and positively charged analytes. Sensitivity of the HFET sensors increases when salt concentration decreases, and the devices also exhibit dose-dependent responses to analyte. Detection of clinically relevant MIG concentrations at physiological salt levels demonstrates the potential for AlGaN devices to be used in development of in vivo biosensors.

Nanoscale adhesion, friction and wear studies of biomolecules on silane polymer-coated silica and alumina-based surfaces

Proteins on biomicroelectromechanical systems (BioMEMS) confer specific molecular functionalities. In planar FET sensors (field-effect transistors, a class of devices whose protein-sensing capabilities we demonstrated in physiological buffers), interfacial proteins are analyte receptors, determining sensor molecular recognition specificity. Receptors are bound to the FET through a polymeric interface, and gross disruption of interfaces that removes a large percentage of receptors or inactivates large fractions of them diminishes sensor sensitivity. Sensitivity is also determined by the distance between the bound analyte and the semiconductor. Consequently, differential properties of surface polymers are design parameters for FET sensors. We compare thickness, surface roughness, adhesion, friction and wear properties of silane polymer layers bound to oxides (SiO2 and Al2O3, as on AlGaN HFETs). We compare those properties of the film–substrate pairs after an additional deposition of biotin and streptavidin. Adhesion between protein and device and interfacial friction properties affect FET reliability because these parameters affect wear resistance of interfaces to abrasive insult in vivo. Adhesion/friction determines the extent of stickage between the interface and tissue and interfacial resistance to mechanical damage. We document systematic, consistent differences in thickness and wear resistance of silane films that can be correlated with film chemistry and deposition procedures, providing guidance for rational interfacial design for planar AlGaN HFET sensors.

Improved Sensitivity of AlGaN/GaN Field Effect Transistor Biosensors by Optimized Surface Functionalization

In this paper, we optimize the AlGaN surface oxidation methods for AlGaN/GaN heterostructure field effect transistor (HFET) biological sensors. Reactive ion etching oxygen plasma, inductively coupled oxygen plasma, and piranha solution are used to oxidize AlGaN surface. After oxidation, X-ray photoelectron spectroscopy and water contact angle measurements are used to check oxidation effectiveness. Labeled streptavidin (SA) molecules are bound to the oxidized surface through linker molecules for comparison of surface modification effectiveness. Schottky diodes are fabricated to investigate the impacts of oxidation processes on electrical properties, such as Schottky barrier heights, sheet carrier concentrations, and interface trap densities. The results show that the inductively coupled plasma oxidation process has a superior behavior compared to the reactive ion etching oxygen plasma and piranha solution oxidation processes. AlGaN/GaN HFET protein sensors fabricated using the inductively coupled plasma oxidation process have exhibited improved sensitivity. An SA solution with the concentration as low as 4.73 pM were successfully detected.

High sensitivity AlGaN/GaN field effect transistor protein sensors operated in the subthreshold regime by a control gate electrode

We demonstrate high sensitivity AlGaN/GaN field effect transistor biosensors with a control gate electrode for streptavidin detection. The device active area is functionalized with 3-Aminopropyltriethoxysilane and N-hydroxysulfosuccinimide-biotin for streptavidin binding. Without any electrochemical side effects, a gate voltage is applied through a Pt control electrode to the solution so that the device operates sensitively in the subthreshold regime. Due to the logarithmic relationship between the channel current and gate voltage in the subthreshold regime, at a concentration of 4.73 pM streptavidin, the device exhibits 9.97% current change in the subthreshold regime compared with the current in phosphate buffered saline solution. In the linear regime, the current change is 0.49% at the same streptavidin concentration.

ImmunoFET feasibility in physiological salt environments

Field-effect transistors (FETs) are solid-state electrical devices featuring current sources, current drains and semiconductor channels through which charge carriers migrate. FETs can be inexpensive, detect analyte without label, exhibit exponential responses to surface potential changes mediated by analyte binding, require limited sample preparation and operate in real time. ImmunoFETs for protein sensing deploy bioaffinity elements on their channels (antibodies), analyte binding to which modulates immunoFET electrical properties. Historically, immunoFETs were assessed infeasible owing to ion shielding in physiological environments. We demonstrate reliable immunoFET sensing of chemokines by relatively ion-impermeable III-nitride immunoHFETs (heterojunction FETs) in physiological buffers. Data show that the specificity of detection follows the specificity of the antibodies used as receptors, allowing us to discriminate between individual highly related protein species (human and murine CXCL9) as well as mixed samples of analytes (native and biotinylated CXCL9). These capabilities demonstrate that immunoHFETs can be feasible, contrary to classical FET-sensing assessment. FET protein sensors may lead to point-of-care diagnostics that are faster and cheaper than immunoassay in clinical, biotechnological and environmental applications.

Interfacial design and structure of protein/polymer films on oxidized AlGaN surfaces

Protein detection using biologically or immunologically modified field-effect transistors (bio/immunoFETs) depends on the nanoscale structure of the polymer/protein film at sensor interfaces (Bhushan 2010 Springer Handbook of Nanotechnology 3rd edn (Heidelberg: Springer); Gupta et al 2010 The effect of interface modification on bioFET sensitivity, submitted). AlGaN-based HFETs (heterojunction FETs) are attractive platforms for many protein sensing applications due to their electrical stability in high osmolarity aqueous environments and favourable current drive capabilities. However, interfacial polymer/protein films on AlGaN, though critical to HFET protein sensor function, have not yet been fully characterized. These interfacial films are typically comprised of protein–polymer films, in which analyte-specific receptors are tethered to the sensing surface with a heterobifunctional linker molecule (often a silane molecule). Here we provide insight into the structure and tribology of silane interfaces composed of one of two different silane monomers deposited on oxidized AlGaN, and other metal oxide surfaces. We demonstrate distinct morphologies and wear properties for the interfacial films, attributable to the specific chemistries of the silane monomers used in the films. For each specific silane monomer, film morphologies and wear are broadly consistent on multiple oxide surfaces. Differences in interfacial film morphology also drive improvements in sensitivity of the underlying HFET (coincident with, though not necessarily caused by, differences in interfacial film thickness). We present a testable model of the hypothetical differential interfacial depth distribution of protein analytes on FET sensor interfaces with distinct morphologies. Empirical validation of this model may rationalize the actual behaviour of planar immunoFETs, which has been shown to be contrary to expectations of bio/immunoFET behaviour prevalent in the literature for the last 20 years. Improved interfacial properties of bio/immunoHFETs have improved bio/immunoHFET performance: better understanding of interfaces may lead to mechanistic understanding of FET sensor properties and to clinical translation of the immunoFET platform.

Rational Enhancement of Nanobiotechnological Device Functions Illustrated by Partial Optimization of a Protein-Sensing Field Effect Transistor

Semiconductor field effect transistors(FETs) are widely used as biosensors, although a potentially powerful application of FET sensing technology (planar immunoFETs sensing proteins at physiological salt concentrations) has long been argued to be intrinsically infeasible. The infeasibility assessment has come under increasing scrutiny of late, and has been found to be lacking on conceptual and empirical grounds. This paper summarizes some, but, by no means all, of the strategies that have been pursued to render the use of immunoFETs, and analogous FET sensors that detect the electrical fields of proteins bound to affinity elements on FET sensing channels (protein-sensing bioFETs), practical in high-salt biological buffers. This paper provides original characterization of oxidized AlGaN surfaces and interfacial polymer/protein films of protein-sensing AlGaN/GaN HFETs. It shows those films to influence significantly FET sensitivity/signal accumulation. The data indicate that re-assessment of the classical assertion of immunoFET infeasibility is long overdue. Beyond substantiating the feasibility of immunoFET operation under solution conditions as found in vivo, data presented here also suggest that transition away from costly AlGaN/GaN HFETs to inexpensive silicon-based immunoMOSFETs may be possible. If so, immunoFETs, dismissed as infeasible 20 years ago, may yet become powerful clinical tools.

Comparative Efficacy and Safety of Triple Therapy (Ramipril, Telmisartan, Hydrochlorothiazide) Vs Dual Anti Hypertensive Therapy (Ramipril or Telmisartan, Hydrochlorothiazide) in Stage 2 Hypertensive Patients

AIM To evaluate the comparative efficacy and safety of ramipril 5mg plus hydrochlorothiazide 12.5mg (R + HCTZ), telmisartan 40mg plus hydrochlorothiazide12.5mg (T + HCTZ) and ramipril 2.5mg plus telmisartan 20mg plus hydrochlorothiazide12.5mg (R + T + HCTZ) in patients with stage 2 hypertension. MATERIALS AND METHODS A prospective, open label, randomized comparative study was conducted to study the comparative efficacy and safety of R+HCTZ (group 1), T+HCTZ (group 2)and R+T+TCTZ (group3) in 88 patients with stage 2 hypertension without co-morbid conditions. Echocardiography was done to assess left ventricular function. Patients were followed up to 24 weeks and any ADR occurring in this period was recorded. RESULTS All the three treatment groups showed significant fall in both systolic and diastolic blood pressure compared to the baseline scores (p<0.0001). Intergroup comparison did not reveal any significant difference. Total number of adverse drug events reported were 15. Group III had higher percentage ADRs. Dry cough (8) was most common ADR. The echocardiography parameters did not change from baseline values with all three treatment regimens. CONCLUSION All three medications were of equal efficacy in patients with stage 2 hypertension without co morbid conditions, failing to prove superiority over each other.

Electrical Detection of Biological Conjugation by AlGaN/GaN Heterostructure Field Effect Transistors

The article presents the electrical detection of streptavidin and monokin induced by interferon gamma proteins and hybridization process of single strand DNA by AlGaN/GaN HFETs. For protein conjugation detection, AlGaN gate surface was functionalized by oxidation, 3-aminopropyltriethoxysilane treatment, and biotinylation using NHS-sulfo-biotin. For streptavidin (STA) detection, at different ionic strengths, the effect of Debye length on detection sensitivity has been demonstrated. For DNA hybridization detection, 12-mer prime ssDNA with matched and mismatched sequences were used as probe and target molecules.