Rangra, Kamaljit

A sensitive and rapid electrochemical sensor has been developed to detect Escherichia coli (E. coli) bacteria that is crucial for ensuring safe drinking water. E. coli significantly contributes to waterborne contamination, driven by overexploitation and insufficient cleanliness around water bodies. This work incorporates synthesis and characterization of graphene oxide (GO), sensor preparation, and sensor testing in the presence of varying E. coli dilutions via H2O2 decomposition. GO is used as a sensing layer and drop casted on the working electrode of screen printed electrode (SPE). The sensor is exposed to different bacterial solutions using varied bacterial concentrations and fixed percent solution of H2O2. The interface of GO and bacterial solution results in a change in potential. The cross-sensitivity tests have also been performed in the presence of chemical compounds found in wastewater samples, Pseudomonas aeruginosa and Citrobacter youngae. The sensor demonstrates a detection limit of 2.8 CFU/mL, with a sensitivity of 5.1 mV-mL/CFU, fast response time and excellent repeatability when tested with E. coli. Its performance has also been assessed by comparing the sensing results for regular tap water, reverse osmosis (RO) water, and deionized water samples. This work paves the way for developing a chip-based system to detect E. coli in water.

For 5 G applications, isolation of better than −40 dB is required to prevent cross-talk between adjacent channels. Isolation of reported Radio Frequency (RF.) Microelectromechanical system (MEMS) switches lie in – 25 to −35 dB. A new improved fabrication process to improve the isolation of the Single Pole Single Throw (SPST) Radio Frequency (RF) switch is proposed in the present work. The measured resonant frequency of the switch is 24.50 GHz, matching the simulated value. The switch's measured insertion loss is better than −0.5 dB at the 24.50 GHz frequency band, which is very promising for 5 G applications. In the OFF state, the isolation of the switch is improved from −35.40 dB to −42.50 dB with an improved fabrication process without altering the switch parameters.

Recognizing the need for a hand-held device capable of quantitatively measuring the concentration of bacteria in water, this paper describes a label-free method for rapid detection of Escherichia coli (E. coli) in water via H2O2 decomposition using screen-printed electrodes (SPE) modified with nanostructured metal oxide layers. The study encompasses sensor preparation, bacteria culture, synthesis and characterization of nanostructures, and development of a readout circuitry for lab prototyping. During sensing measurements, the bacteria are first made to interact with H2O2 and subsequently, the H2O2 solution is exposed on the sensing surface. The electrochemical sensors are fabricated by modifying the working electrode of SPE with nanostructured metal oxide layers of MnO2 and TiO2 as these play a crucial role in the detection of E. coli in water. The sensing experiments of MnO2-modified SPE show a significant response to bacteria with a sensitivity of 0.82 mV.mL/log CFU and a limit of detection (LOD) of 1.8 CFU/mL, while the TiO2-modified SPE exhibits a linear response over a wide range of bacterial concentrations with a sensitivity of 1.12 mV·mL/log CFU and a limit of detection of 2.23 CFU/mL. Both sensors demonstrate a rapid response, stability, repeatability, and a recovery time of 70 ms. Additionally, selectivity with respect to other bacteria, wastewater components such as glucose, ammonium sulfate, and sodium carbonate, and testing with RO, DI, and tap water samples are conducted to evaluate the sensors’ performance. A detailed sensing mechanism has been developed to comprehend the results, including chemical and biological reactions, metal oxide interfaces, morphology, and other surface studies of the sensing surface. A prototype comprising a sensor chip, an Arduino board, and other necessary circuit components is tested with various bacterial solutions. This enables its use for on-field rapid detection of bacteria in water using smaller volumes and a portable system.

Quadrupole mass spectrometry (QMS) offers better resolution, selectivity and sensitivity than the metal-oxide, field effect transistors and thermal-based gas sensors. However, existing QMS systems are unsuitable for field applications. The miniaturized QMS requires dimensionally scaled components with comparable performance to the conventional bulky systems. For a portable quadrupole mass spectrometry, a compact focusing ion system is required to transfer the maximum number of ions from the ion source to the filter. The present paper discusses the design of a miniature focusing Einzel lens and the effect of design parameters on its performance. The three-cylindrical axially symmetric compact Einzel lens assembly was designed using commercially available software. The relationship between the design parameters is explored for compact and low-powered ion optics. The beam focal length was tuned by varying the bias voltage. The dimensions, as well as voltages across the Einzel lens, were reduced significantly to open a new way for portable point-of-care applications. At an applied voltage of 70 V, the focal length of the ions is 11 mm without being scattered, which is favorable for a portable quadrupole mass filter. The designed Einzel lens was fabricated using micromachining techniques and characterized at a vacuum of 3.05 × 10−4 mbar. The developed lens system shows a current output of 0.114 µA at 72 V lens voltage. A current of 94.8 µA is observed with a background noise of 0.01 µA for the system with nitrogen (28 amu) as the sample.

This paper presents an analytical approach to envisage a suitable operating pressure and investigate the effect of squeezed-film damping on the transient response of a micromirror of size 200 μm × 200 μm and a deflection of 2.5 μm for space-based multiobject spectroscopy. While most MEMS devices are vacuum packaged to achieve a high Q and fast switching, the same may not be true for applications that are prone to vibrations and shocks. At small pressures, the micromirror can produce undesired deflections and oscillations, and hence, a high-pressure operation becomes necessary to alleviate these effects.The operating pressure and its effect on the transient response of the micromirror are investigated by solving linearized Reynold’s equation and dynamic equation of motion using the numerical iteration method. The result shows an overdamped response above 10 kPa pressure. At 101 kPa, the micromirror exhibits a switching and release time of 102 μs and 95 μs, respectively. The analytical results are very close to the FEM results with a deviation of 8%. The result shows that operating a micromirror at atmospheric pressure serves the dual purpose of dispensing away with the requirement of vacuum packaging and providing immunity from vibrations and oscillation.