Green-Synthesized Amino Carbons for Impedimetric Biosensing of E. coli O157:H7.

This study describes the synthesis of amino-functionalized carbon nanoparticles derived from biopolymer chitosan using green synthesis and its application toward ultrasensitive electrochemical immunosensor of highly virulent Escherichia coli O157:H7 (E. coli O157:H7). The inherent advantage of high surface-to-volume ratio and enhanced rate transfer kinetics of nanoparticles is leveraged to push the limit of detection (LOD), without compromising on the selectivity. The prepared carbon nanoparticles were systematically characterized by employing CO2-thermal programmed desorption (CO2-TPD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-visible), and transmission electron microscopy (TEM). The estimated limit of detection of 0.74 CFU/mL and a sensitivity of 5.7 ((ΔRct/Rct)/(CFU/mL))/cm2 in the electrochemical impedance spectroscopy (EIS) affirm the utility of the sensor. The proposed biosensor displayed remarkable selectivity against interfering species, making it well suited for real-time applications. Moreover, the chitosan-derived semiconducting amino-functionalized carbon shows excellent sensitivity in a comparative analysis compared to highly conducting amine-functionalized carbon synthesized via chemical modification, demonstrating its vast potential as an E. coli sensor.

Toll-like receptor-immobilized carbon paste electrodes with plasma functionalized amine termination: Towards real-time electrochemical based triaging of gram-negative bacteria.

Chronic wounds caused due to bacterial biofilms are detrimental to a patient, and an immediate diagnosis of these bacteria can aid in an effective treatment, which is still an unmet clinical need. An instant and accurate identification of bacterial type could be made by utilizing the Toll-Like Receptors (TLRs) combined with Myeloid Differentiation factor 2 (MD-2). Given this, we have developed an electrochemical sensing platform to identify the gram-negative (gram-ve) bacteria using TLR4/MD-2 complex. The nonthermal plasma (NTP) technique was utilized to functionalize amine groups onto the carbon surface to fabricate cost-effective carbon paste working electrodes (CPEs). The proposed electrochemical sensor platform with a specially engineered electrochemical cell (E-Cell) identified the Escherichia coli (E. coli) in a wide linear range of 1.5×10° - 1.5×106 C.F.U./mL, accounting for a very low detection limit of 0.087 C.F.U./mL. The novel and cost-effective sensor platform identified gram-ve bacteria predominantly in a mixture of gram positive (gram+ve) bacteria and fungi. Further, towards real-time detection of bacteria and point-of-care (PoC) applications, the effect of the pond water matrix was studied, which was minimal, and the sensor could identify E. coli concentrations selectively, showing the potential application of the proposed platform towards real-time bacterial detection.

Hybridization of Co3S4 and Graphitic Carbon Nitride Nanosheets for High-performance Nonenzymatic Sensing of H2O2.

The development of efficient H2O2 sensors is crucial because of their multiple functions inside and outside the biological system and the adverse effects that a higher concentration can cause. This work reports a highly sensitive and selective non-enzymatic electrochemical H2O2 sensor achieved through the hybridization of Co3S4 and graphitic carbon nitride nanosheets (GCNNS). The Co3S4 is synthesized via a hydrothermal method, and the bulk g-C3N4 (b-GCN) is prepared by the thermal polycondensation of melamine. The as-prepared b-GCN is exfoliated into nanosheets using solvent exfoliation, and the composite with Co3S4 is formed during nanosheet formation. Compared to the performances of pure components, the hybrid structure demonstrates excellent electroreduction towards H2O2. We investigate the H2O2-sensing performance of the composite by cyclic voltammetry, differential pulse voltammetry, and amperometry. As an amperometric sensor, the Co3S4/GCNNS exhibits high sensitivity over a broad linear range from 10 nM to 1.5 mM H2O2 with a high detection limit of 70 nM and fast response of 3 s. The excellent electrocatalytic properties of the composite strengthen its potential application as a sensor to monitor H2O2 in real samples. The remarkable enhancement of the electrocatalytic activity of the composite for H2O2 reduction is attributed to the synergistic effect between Co3S4 and GCNNS.

Plasma Functionalized Carbon Interfaces for Biosensor Application: Toward the Real-Time Detection of Escherichia coli O157:H7.

Nonthermal plasma, a nondestructive, fast, and highly reproducible surface functionalization technique, was used to introduce desired functional groups onto the surface of carbon powder. The primary benefit is that it is highly scalable, with a high throughput, making it easily adaptable to bulk production. The plasma functionalized carbon powder was later used to create highly specific and low-cost electrochemical biosensors. The functional groups on the carbon surface were confirmed using NH3-temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) analysis. In addition, for biosensing applications, a novel, cost-effective, robust, and scalable electrochemical sensor platform comprising in-house-fabricated carbon paste electrodes and a miniaturized E-cell was developed. Biotin-Streptavidin was chosen as a model ligand-analyte combination to demonstrate its applicability toward biosensor application, and then, the specific identification of the target Escherchia coli O157:H7 was accomplished using an anti-E. coli O157:H7 antibody-modified electrode. The proposed biosensing platform detected E. coli O157:H7 in a broad linear range of (1 × 10-1-1 × 106) CFU/mL, with a limit of detection (LOD) of 0.1 CFU/mL. In addition, the developed plasma functionalized carbon paste electrodes demonstrated high specificity for the target E. coli O157:H7 spiked in pond water, making them ideal for real-time bacterial detection.

ZnO nanoparticles embedded silk fibroin-a piezoelectric composite for nanogenerator applications.

This paper demonstrates a flexible nanogenerator (NG) using Silk-Zinc Oxide (ZnO) composite by exploiting the inherent piezoelectric properties of silk and ZnO. A direct precipitation method was employed to synthesize Zinc Oxide nanoparticles (NPs). Silk-ZnO composite film was then prepared by spin-coating the homogenous silk-ZnO solution. The composition and morphology of silk-ZnO composite were analyzed using various standard characterization procedures. The biocompatibility study of the composite film was also performed through cell viability testing. The utility of as prepared composites was demonstrated through the fabrication of piezoelectric nanogenerator. This hybrid nanogenerator was capable to generate a maximum open circuit voltage of 25 V (peak to peak value) in the bending state for a specific ZnO concentration. The output response of the nanogenerator exhibited a good correlation with the bending angle of the device. A peak outputpower density of 6.67 mW cm-3was achieved from the nanogenerator. The fabricated prototype is efficient to light-up commercial red LEDs and to harvest energy from human body movement. The piezoelectric coefficient (d33) of silk-ZnO composite film was also experimentally figured out.

A Hybrid Bipolar Active Charge Balancing Technique with Adaptive Electrode Tissue Interface (ETI) Impedance Variations for Facial Paralysis Patients.

Functional electrical stimulation (FES) is a safe, effective, and general approach for treating various neurological disorders. However, in the case of FES usage for implantable applications, charge balancing is a significant challenge due to variations in the fabrication process and electrode tissue interface (ETI) impedance. In general, an active charge balancing approach is being used for this purpose, which has limitations of additional power consumption for residual voltage calibration and undesired neurological responses. To overcome these limitations, this paper presents a reconfigurable calibration circuit to address both ETI variations and charge balancing issues. This reconfigurable calibration circuit works in two modes: An impedance measurement mode (IMM) for treating ETI variations and a hybrid charge balancing mode (HCBM) for handling charge balance issues. The IMM predicts the desired stimulation currents by measuring the ETI. The HCBM is a hybrid combination of electrode shorting, offset regulation, and pulse modulation that takes the best features of each of these techniques and applies them in appropriate situations. From the results, it is proved that the proposed IMM configuration and HCBM configuration have an optimal power consumption of less than 44 µW with a power ratio ranging from 1.74 to 5.5 percent when compared to conventional approaches.

Development of robust, ultra-smooth, flexible and transparent regenerated silk composite films for bio-integrated electronic device applications.

Regenerated Silk Fibroin (RSF) films are considered promising substrate candidates primarily in the field of bio-integrated electronic device applications. The key issues that ought to be addressed to exploit the inherent advantages of silk thin films include enhancing their flexibility and chemical durability. Such films find a plethora of applications, the significant one being conformal, transparent microelectrode arrays. Elevated temperatures that are regularly used in lithographic processes tend to dehydrate RSF films, making them brittle. Furthermore, the solvents/etchants used in typical device fabrication results in the formation of micro-cracks. This paper addressed both these issues by developing composite films and studying the effect of biodegradable additives in enhancing flexibility and chemical durability without compromising on optical transparency and surface smoothness. Through our rigorous experimentation, regenerated silk blended with Polyvinyl Alcohol (Silk/PVA) is identified as the composite for achieving the objectives. Furthermore, the Cyto-compatibility studies suggest that Silk/PVA, along with all other silk composites, have shown above 80% cell viability, as verified using L929 fibroblast cell lines. Going a step further, we demonstrated the successful patterning of 32 channel optically transparent microelectrode array (MEA) pattern, with a minimum feature size of 5 µm above the free-standing and optically transparent Silk/PVA composite film.

Electrospun CNT embedded ZnO nanofiber based biosensor for electrochemical detection of Atrazine: a step closure to single molecule detection.

In this study we have reported the design and development of a facile, sensitive, selective, and label-free electrochemical sensing platform for the detection of atrazine based on MWCNT-embedded ZnO nanofibers. Electrospun nanofibers were characterized using scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), UV-Visible spectroscope (UV-VIS), and Fourier-transform infrared spectroscope (FTIR). Electrochemical properties of MWCNT-ZnO nanofiber-modified electrodes were assessed using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Binding event of atrazine to anti-atrazine antibody, which immobilized on nanofiber-modified electrode via EDC and NHS chemistry, was transduced with EIS. Due to high conductivity, surface area, and low bandgap of MWCNT-ZnO nanofibers, we have achieved the sensitivity and limit of detection (LoD) of sensor as 21.61 (KΩ µg-1 mL-1) cm-2 and 5.368 zM for a wide detection range of 10 zM-1 µM. The proposed immunosensing platform has good stability, selectivity, repeatability, and reproducibility, and are less prone to interference.

A miniaturized electrochemical platform with an integrated PDMS reservoir for label-free DNA hybridization detection using nanostructured Au electrodes.

We report the fabrication and characterization of a miniaturized electrochemical platform for the label-free detection of DNA hybridization. The proposed platform is fabricated using microfabrication and electrodeposition techniques. Comprising a Ti working electrode with electrodeposited Au nanostructures, and Pt/Au pseudo-reference and counter electrodes, the device accounts for a limit of detection of 0.97 fM and a sensitivity of 20.78 (µA µM-1) cm-2 with respect to Dengue virus specific consensus primer detection in the range of 10 fM-1 µM. Here, the incorporation of nanostructured Au in the active sensing area not only enhances the current response by increasing the overall surface area, but it also facilitates facile probe DNA immobilization by gold-thiol self-assembly. We have used differential pulse voltammetry analysis in this study to monitor the changes in reaction kinetics with respect to target hybridization. Furthermore, the evaluation of reproducibility of the biosensor and its selectivity against interference has yielded acceptable outcomes. Additionally, in order to evaluate the system's selectivity, we have successfully distinguished PCR amplified wild type and mutant target DNAs corresponding to the BRCA1 specific gene. Here, the mutant and the wild type target DNAs differ by a two base deletion, and the fact that the system is able to differentiate even such minute dissimilarities under hybridization conditions is indicative of its superior performance.

Chemiresistive DNA hybridization sensor with electrospun nanofibers: A method to minimize inter-device variability.

Chemiresistive platforms are best suited for developing DNA hybridization detection systems, owing to their ease of fabrication, simple detection methodology and amenability towards electronics. In this work, we report development of a generic, robust, electrospun nanofiber based interdigitated chemiresistive platform for DNA hybridization detection. The platform comprises of interdigitated metal electrodes decorated with electrospun nanofibers on the top. Two approaches viz., drop casting of graphene doped Mn2O3 nanofibers (GMnO) and direct electrospinning of polyaniline/polyethylene oxide (PANi/PEO) composite nanofibers, have been utilized to decorate these electrodes. In both approaches, inter-device variability, a key challenge for converting this proof-of-concept into a tangible prototype/product, has been addressed using a shadow masking technique. Consequently, the relative standard deviation for multiple PANi/PEO nanofiber based chemiresistors has been brought down from 17.82% (without shadow masking) to 4.41% (with shadow masking). The nanofibers are further modified with single-stranded probe DNAs, to capture a desired hybridization event. To establish the generic nature of the platform, detection of multiple target DNAs has been successfully demonstrated. These targets include dengue virus specific consensus primer (DENVCP) and four DNAs corresponding to Staphylococcus aureus specific genes, namely nuc, mecA, vanA and protein A. The chemiresistive detection of DENVCP has been performed in the concentration range of 10 fM - 1 µM, whereas the detection of the other targets has been carried out in the range of 1 pM - 1 µM. Using a 3σ method, we have estimated the limit of detection for the chemiresistive detection of DENVCP to be 1.9 fM.

One step biofunctionalized electrospun multiwalled carbon nanotubes embedded zinc oxide nanowire interface for highly sensitive detection of carcinoma antigen-125.

Ovarian cancer is the most leading cause of cancer-related death in women . The carcinoma antigen-125, which is found on the surface of many ovarian cancer cells is known to be a gold standard clinical biomarker associated with life-threatening gynecological malignancy. In this work, we demonstrate a novel biosensor platform based on multiwalled carbon nanotubes embedded zinc oxide nanowire for the ultrasensitive detection of carcinoma antigen-125. Label free detection of the carcinoma antigen-125 was accomplished by differential voltammetry technique that demonstrated excellent sensitivity (90.14µA/(U/mL)/cm2) with a detection limit of 0.00113UmL-1 concentration. The fabricated immunosensor exhibits good performance with wider detection range (0.001UmL-1-1kUmL-1), reproducibility, selectivity, acceptable stability, and thus is a potential cost-effective methodology for point-of-care diagnosis. The multiwalled carbon nanotubes (MWCNTs) embedded highly oriented zinc oxide (ZnO) nanowires were synthesized by simple, low cost electrospinning technique. Compared to pure ZnO nanowires, electrochemical activity of MWCNTs embedded ZnO nanowires was found to be much higher. The calcination temperature was optimized to avoid any decomposition of the CNTs and to obtain multiwalled carbon nanotubes embedded highly crystalline ZnO nanowires. The salient feature of this biosensing platform is that one step calcination process is enough to create the functional groups on MWCNT-ZnO nanowire surface that are effective for the covalent conjugation of antibody without further surface modification. To the best of our knowledge, this is the first report on MWCNT-ZnO nanowire based immunosensor explored for the detection of cancer biomarker.

A comprehensive approach for milk adulteration detection using inherent bio-physical properties as 'Universal Markers': Towards a miniaturized adulteration detection platform.

This paper proposes a novel milk quality detection approach based on utilization of inherent biophysical properties as 'markers' for adulteration. Unlike the traditional adulterant-specific approaches, this method is generic and universal. It exploits the change in innate milk properties, such as electrical conductivity and pH, upon addition of adulterants as a transduction mechanism for detecting milk adulteration. In this work, adulteration with more than 10 commercially known hazardous adulterants is detected by monitoring the changes in milk electrical conductivity and pH. The electrical parameters for pure milk were standardized using AC impedance-spectroscopy with glassy carbon working electrode and platinum counter/reference electrode at a potential of 0.3V and in the frequency range of 1Hz-1MHz. The experiments were repeated using gold-electrodes fabricated on glass-substrate as a first step towards developing a miniaturized platform. The concept of a 'unified-universal-marker' for successful prediction of adulteration is accentuated in this work.

Ultrasensitive, Label Free, Chemiresistive Nanobiosensor Using Multiwalled Carbon Nanotubes Embedded Electrospun SU-8 Nanofibers.

This paper reports the synthesis and fabrication of aligned electrospun nanofibers derived out of multiwalled carbon nanotubes (MWCNTs) embedded SU-8 photoresist, which are targeted towards ultrasensitive biosensor applications. The ultrasensitivity (detection in the range of fg/mL) and the specificity of these biosensors were achieved by complementing the inherent advantages of MWCNTs such as high surface to volume ratio and excellent electrical and transduction properties with the ease of surface functionalization of SU-8. The electrospinning process was optimized to precisely align nanofibers in between two electrodes of a copper microelectrode array. MWCNTs not only enhance the conductivity of SU-8 nanofibers but also act as transduction elements. In this paper, MWCNTs were embedded way beyond the percolation threshold and the optimum percentage loading of MWCNTs for maximizing the conductivity of nanofibers was figured out experimentally. As a proof of concept, the detection of myoglobin, an important biomarker for on-set of Acute Myocardial Infection (AMI) has been demonstrated by functionalizing the nanofibers with anti-myoglobin antibodies and carrying out detection using a chemiresistive method. This simple and robust device yielded a detection limit of 6 fg/mL.

A highly sensitive self assembled monolayer modified copper doped zinc oxide nanofiber interface for detection of Plasmodium falciparum histidine-rich protein-2: Targeted towards rapid, early diagnosis of malaria.

Rapid, ultrasensitive diagnostic/triaging kits for early detection of malarial parasites are critical for prevention of malarial epidemic, especially in developing and tropical countries. Unlike traditional microscopic diagnosis, these kits rely on the detection of antigens specific to malarial parasites. One such antigen which is routinely used in these diagnostic kits is Histidine-rich protein-2; a protein synthesized and released into the blood stream by the parasite Plasmodium falciparum. In this paper, we demonstrate an ultrasensitive nanobiosensor detection platform for Histidine-rich protein-2 having a limit of detection of attogram/ml. This nanobiosensor platform comprises of Mercaptopropylphosphonic acid functionalized copper doped zinc oxide nanofibers synthesized by electrospinning technique. Ultrasensitivity of attogram/ml can be attributed to the complimentary effects of Mercaptopropylphosphonic acid and copper doping in zinc oxide. Mercaptopropylphosphonic acid enhances the functional groups required for immobilizing antibody. Copper doping in zinc oxide not only increases the conductivity of the nanofibers but also pre-concentrates the target analyte onto the Mercaptopropylphosphonic acid treated nanofiber surface due to inherent electric field generated at the copper/zinc oxide heterojunction interface. The impedimetric detection response of copper-doped zinc oxide nanofiber modified electrode shows excellent sensitivity (28.5 kΩ/(gm/ml)/cm(2)) in the detection ranges of 10 ag/ml-10 µg/ml, and a detection limit of 6 attogram/ml. In addition, the proposed biosensor is highly selective to targeted HRP2 protein with a relative standard deviation of 1.9% in the presence of various interference of nonspecific molecules. To the best of our knowledge, this biosensor shows the lowest detection limit of malarial parasites reported in the literature spanning different nanomaterials and different detection mechanisms. Since the nanobiosensor platform is based on immunoassay technique, with a little modification, it can be extended for developing point-of-care diagnostic devices for several biomarkers of importance.

Fabrication of SU-8 based Capacitive Micromachined Ultrasonic Transducer for low frequency therapeutic applications.

In this paper we present a simple post-CMOS compatible sacrificial release method of fabricating SU-8 based Capacitive Micromachined Ultrasonic Transducer (CMUT) for low frequency therapeutic applications. CMUTs fabricated with Silicon Nitride and Silicon Dioxide lay constraints in terms of area and power consumption especially in the low frequency range. Fabrication of these devices need complex high temperature processes that makes them incompatible for post-CMOS processing. Analytical modeling shows that SU-8 based CMUT consumes less area (below 25%) and power compared to Silicon Nitride and Silicon Dioxide based CMUTs. The proposed fabrication method overcomes inherent disadvantages of sacrificial release method by providing uniformity in air gap and reducing the possibility of stiction.

A low power, area efficient fpga based beamforming technique for 1-D CMUT arrays.

A low power area efficient digital beamformer targeting low frequency (2MHz) 1-D linear Capacitive Micromachined Ultrasonic Transducer (CMUT) array is developed. While designing the beamforming logic, the symmetry of the CMUT array is well exploited to reduce the area and power consumption. The proposed method is verified in Matlab by clocking an Arbitrary Waveform Generator(AWG). The architecture is successfully implemented in Xilinx Spartan 3E FPGA kit to check its functionality. The beamforming logic is implemented for 8, 16, 32, and 64 element CMUTs targeting Application Specific Integrated Circuit (ASIC) platform at Vdd 1.62V for UMC 90nm technology. It is observed that the proposed architecture consumes significantly lesser power and area (1.2895 mW power and 47134.4 µm(2) area for a 64 element digital beamforming circuit) compared to the conventional square root based algorithm.

A low pull-in SU-8 based Capacitive Micromachined Ultrasonic Transducer for medical imaging applications.

In this paper we present a thorough analysis of a low pull-in voltage Capacitive Micromachined Ultrasonic Transducer (CMUT) using SU-8 as the membrane material. It is designed to operate at 1 MHz frequency that has a wide range of applications including the imaging of deeper organs. We also propose a simple state-of-the-art fabrication methodology for the same. As compared to the standard Silicon Nitride CMUTs, the proposed structure gives the same electromechanical coupling coefficient with lower membrane dimensions and low pull-in voltage which in turn results in reduced area and power consumption. Moreover the proposed fabrication methodology is a low temperature process which makes it CMOS compatible.