Dhanekar, Saakshi

Detection of E. coli bacteria is imperative when it comes to potable water cleanliness and human health. E. coli when present in drinking water can cause ill health and its presence in urine is an indication of Urinary Tract Infection (UTI). This paper reports the development of rapid, easy to use, and low cost electrochemical sensor for detection of E.coli. The sensor is fabricated by drop casting graphene oxide (GO) on the screen printed carbon electrodes. Different bacteria dilutions were mixed with a fixed concentration of H2O2. Graphene oxide sheets allow for the indirect detection of bacteria by reducing the remaining concentration of H2O2 following the bacterial catalytic activity. This work presents GO synthesis, characterization, sample preparation and bacterial testing using H2O2 degradation. The sensor provides a response within a range of 0 to $2.7 \times 10^{3}$ CFU/mL and has a detection limit of 6.3 CFU/mL. The amount of time required for both response and recovery of the sensor is measured in milliseconds.

We present the development of sensor array using commercial chemiresistive sensors for detecting volatile organic compounds (VOCs) which are dominant in breath during certain health conditions and as indoor pollutants. The sensors array output showed different voltages in response to varying concentration of individual VOCs and different ratios of VOCs in a mixture. The responses from the sensors array were processed using Principal Component Analysis (PCA) which shows that the developed sensors array can work to identify individual VOC from the mixture. The authors are now working on in-house sensors to use these in an array form with exposure to more VOCs and aim to develop an electronic nose system for sensing the presence of VOCs in breath for human health and indoor environment monitoring.

Wearable dosimeters form an essential part of the personnel protection scheme in work spaces such as defence, nuclear establishments, and medical fields with radiation hazard. In the current scenario where use of high energy ionizing radiation sources (nuclear sources) is indispensable, the need of radiation detectors is mandatory for measuring the dose received by the person exposed in his work space and also measure the dose for patients where nuclear radiation is used for treatment. Wearable dosimeters need to have some special requirements apart from being accurate, precise, and robust. These need to be light in weight and should cause no harm to the human body while it is touching the body or apparels. This paper comprises an introduction to dosimeters, key characteristics, important techniques used for detection of neutrons and X-rays and also mentions about a few potential companies involved in developing wearable dosimeters in these application areas. The techniques have been collated, described, compared and the need to detect neutrons and X-rays has been expressed keeping in mind the demand from the defence and medical disciplines. This review also contains artificial intelligence and internet of things which form the basis of trending and upcoming wearable dosimeters.

In the present work, we report design, fabrication and testing of a novel DC MEMS switch incorporating a self-encapsulated and recessed micro-cantilever beam. Wafer level anodic bonding with press-on contacts between silicon and glass is used innovatively to secure the recessed cantilever beam from one side. The cantilever is made of single crystal silicon in a recessed cavity whereas actuating electrode and signal lines are formed on corning glass. Anodic bonding provides “press on contacts” between silicon and glass plate and also secures the cantilever beam in the recessed cavity in silicon. The signal lines and pull-in electrode are formed on the glass plate using aluminium metallization while the cantilever has a gold pad at its tip. The anodic bonding provides three major advantages (i) it encapsulates the fragile beam and thus protects it from damage during dicing and packaging process (ii) it provides press-on contact between signal lines on glass plate and bonding pads on silicon (iii) it makes the beam optically visible. The devices were simulated using COMSOL multiphysics software and the results were compared with experimentally measured values. The cantilever based switch operates at low actuation voltage (average ~ 12 V) indicating that it can be used for power electronic circuits and various other applications.

The domain of optoelectronics has wide scope and plays a major role in the design of smart electronics for real-world applications. In this paper we propose a WO3 based Field Effect Transistor (FET) device that functions as a phototransistor. The proposed device consists of 80 nm thin film of WO3 deposited using Radio Frequency (RF) sputter deposition technique. The synthesized material was characterized to investigate structural, morphological and optical properties. The fabricated FET exhibits ambipolar behaviour and it provides a great response for making a promising device for photo sensing applications. The proposed WO3-FET based phototransistor presents the photo-to-dark current ratio (PDCR) in the order of 10 under 650 nm illumination. Furthermore, the device shows repeatable results with higher stability. Additionally, the remarkable advantage proposed in this paper is the device being wafer scalable which increases the competence for mass manufacturing the devices.

Applications of photo detectors in various areas have greatly motivated its research and development. This paper reports a heterojunction based porous silicon (PS) and TiO2hetero junction of the type of gold-PS-TiO2-gold (metal semiconductor metal) structure. The response of the photo detector is tested in presence of room light, flash light and laser (wavelength between 630-670 nm) and sensitivity is found to be 66.66%, 84% and 126% respectively. Other sensor parameters have also been studied; for example, responsivity, response and recovery time. Further, the sensor output is integrated to a cloud-based IoT platform. A demonstration of sensing and control in an IoT network with use of a photodetector has been portrayed. This type of arrangement is found to be beneficial for applications where frequent human intervention is not possible.

The role of indium trioxide (In2O3) decorated Si nanowires (SiNWs) based resistive sensor for selective detection of ethanol vapors at near room temperature has been successfully demonstrated. SiNWs samples were synthesized using metal assisted chemical etching technique and these were decorated by a thin film of indium followed by annealing. The sensing response was captured by measuring the change in resistance of the sensing layer using a Cr-Au inter-digitated-electrode (IDE) structure formed on top of the sensing layers. All sensors were tested for ethanol, acetone, iso-propanol (IPA), xylene, benzene and toluene vapours in the wide concentration range of 5-500 ppm and at different temperatures. Sensors based on SiNWs alone had displayed higher response towards acetone vapours whereas after heterojunction formation with In2O3, significant sensitivity to ethanol was depicted. In2O3 decorated SiNWs resulted in significant enhancement of the sensor response% towards ethanol at near room temperature. Minimum detection of ethanol at 50 ppm and 10 ppm was portrayed by SiNWs and In2O3/SiNWs based sensors respectively. It was concluded that sensing behaviour was a consequence of combinatory effect produced by the presence of both SiNWs and In2O3. A simple explanation with device schematic and band diagrams of the material are proposed to describe the sensing mechanism. This study demonstrates the significance of surface treatment of SiNWs and the role of heterostructures for tuning the sensing properties and development of wafer scalable sensors.

This work presents the design aspects of Mach Zehnder Interferometer (MZI) based biosensors for bio-molecular detection. The effects of physical dimensions in the wave propagation in a Mach Zehnder Interferometer (MZI) has been studied using Comsol Multiphysics software. The design is proposed for development of biosensor for detection of lipoarabinomannan (LAM) antigen. The MZI structure has been realized using Y-junctions with s-bend configuration and cut-off bend radius is determined. This study is required for nanoscale fabrication and to achieve high sensitivity in biosensing application especially in detection of TB in early stages through urine samples.

This letter presents a human nose breath sensor based on partially reduced graphene oxide (PrGO) operating at room temperature. The sensing layer is developed by drop casting graphene oxide (GO) on a glass substrate with silver electrodes and was partially reduced thermally at 150 °C. The results with GO film have also been compared. The developed sensor was successful in detecting various breath patterns by observing the frequency and amplitude of the sensor's current change to exposure to nose breath. The sensor was capable of differentiating between slow, normal, and fast breathing based on the response and recovery times. This sensor can be very useful for characterization of diseases, such as asthma, chronic obstructive pulmonary disease, sleep apnea, and cardiac arrest, where the person's respiration rate is measured.

Breath-based volatile organic compound (VOC) sensors are important for developing a non-invasive way of disease detection. Currently used blood-based devices for the detection of disease are invasive and cause discomfort to the patient. This paper reports a non-invasive and sensitive method of disease detection which depends on thermal actuation in a MEMS device and the capacitive readout circuit of the sensor which is verified in proteus software. The sensor design simulation, static and modal analysis to study the top plate displacement and the device's vibration frequency is done using CoventorWare software. The simulation study depicts a linear response by the sensor for a wide range of VOC concentrations with a sensitivity of.54μm/Pa. The relation of sensor response with various other parameters like sensing layer thickness, length and width of the beam, perforation size of the top layer, distance between top and bottom layer, the temperature profile of the micro heater, etc. are also described.It is observed that the top plate supported by four beams is more sensitive to applied load as compared to ring-supported. By functionalization of the sensing layer, this device can be extremely useful in the detection of specific diseases using breath biomarkers, as the tool for sensing, in point-of-care applications.