Microcantilever-based sensor platform has attracted a lot of attention over the time in detection of a variety of molecules due to their miniaturized dimensions. Sensitivity enhancement is an important aspect of such sensors, especially when used for point-of-care diagnostic purpose. However, the major concern while operating these sensors in deflection mode is their sensitivity which mainly relies on selective chemical modification protocols employed on these sensor surfaces. One of the ways of getting better sensitivity is through asymmetric (one side) biofunctionalization of the sensor surface. In the presented work here, we have demonstrated a novel approach of asymmetric biofunctionalization of proteins in overall sensitivity enhancement of piezoresistive silicon nitride-oxide microcantilever sensor platform inside a flow chamber. Herein, using our developed surface chemistry, asymmetrically biofunctionalized microcantilevers first exhibited a greater electrical response in terms of piezoresistance change than their symmetric counterpart in the detection of human immunoglobulins (HIgGs) protein. Finally, these microcantilevers were employed to exhibit the enhanced sensitivity towards the detection of a crucial cardiac marker protein, i.e. Troponin-I (cTnI) down to 250 ng ml ⁻¹ using asymmetric biofunctionalization process. This study shows that the developed asymmetric biofunctionalization methodology may be used as a general protocol to detect other important biomarkers of clinical applications with improved sensitivity.

In this paper, we have studied the curvature transition of hydrophobe-water interface. This transition has been observed to take place from curved-to-flattened in extreme alkaline conditions. An analytical model involving the charging-induced electrochemomechanical changes has been developed to qualitatively explain such transitions of oil-water interfaces. Two types of studies have been conducted for this work, one with liquid-liquid interface and another with solid-liquid interface respectively. The study done with liquid-liquid interface involved the use of commercially available mustard oil that was poured over the liquids of varying pH. Further investigations done with solid-liquid interface showed the abrupt transition of the sessile drop's shape beyond a certain pH, when the drop was put on a glass slide smeared with wax. Thus, we have successfully demonstrated that the pH range of the liquids can be determined by using very simple and easily available household materials like mustard oil and wax. The detected pH range was unity (range: 11.0-12.0) in our work. It would help the researchers to determine whether a given liquid has a pH greater than or less than a certain value, depending on the choice of the oil/hydrophobic surface, just by visual inspection with no sophisticated instruments required and minimum costs incurred.

Dynamic sensing using microcantilevers has held the centre stage for a long time in biomolecular detection. In this work, we have reported a comparative study of dynamic responses of asymmetric (top or bottom surface) and symmetric (both top and bottom surfaces) modifications (biofunctionalization) of silicon nitride/oxide microcantilevers. For the first time, surface stress (in terms of surface energy/area) has been shown to govern the change in resonant frequency by studying the dynamic responses of asymmetrically and symmetrically modified microcantilevers using a conventional laser doppler vibrometer. The resonant frequency of asymmetrically modified microcantilever was found to be lower than that of symmetrically modified one by a magnitude of ~0.4 kHz. Also, it was observed that the amplitude of oscillation increased from symmetrically modified to asymmetrically modified microcantilever. Consequentially, we have reported (by means of mathematical calculations and nanoindentation experiments) the increase in flexural rigidity as well as surface stress from symmetric modification to the asymmetric one. Owing to the decrease in the resonant frequencies as well as downward bending of microcantilevers, we conclude that compressive surface stress is developed after surface modifications. This work will be of immense interest to the researchers working in the field of dynamic sensing using MEMS-based sensors.

Coffee and caffeine have been used as solar absorbers and also to increase the thermal stability and efficiency of perovskite solar cells. In this work, we report the sensing of extremely alkaline pH by colloidal coffee solution aided by generation of an optical absorption band in the near-UV region. This generation of absorption band could be explained by the orientation induced dipole-dipole interactions arising from differing caffeine-solvent interactions with varying pH. Such a generation leads to the lowering of direct as well as indirect bandgaps from 4 eV-->2.8 eV& 3.4 eV-->2.5 eV, respectively. We also estimate the changes in optical energy storage efficiency, inferring it to be highest for pH 11 having the highest intensity of the generated absorption band (λ_abs≈360 nm). With these observations and further deductions, the work reported in this paper would be of immense interest to the researchers working in the field of development of chemical pH sensors and also in the development of novel UV absorbers.