A novel method has been developed for the encapsulation of gold nanoparticles (AuNPs) and glucose oxidase (GOx) together into the cavity of a zeolitic imidazolate framework (ZIF-8) in aqueous media and subsequently used for amperometric glucose sensing application. ZIF-8 is a highly efficient, stable (thermally and chemically) microstructure and possesses a large surface area with a unique cavity to accommodate both AuNPs and GOx. The as-synthesized composite is thoroughly characterized by various physicochemical methods and confirms the uniform distribution of AuNPs within the metal−organic framework cavity. The presence of highly conducting AuNPs enhances the activity of GOx and facilitates the mediator-free tandem electrocatalytic reactions of both glucose oxidation and oxygen reduction. Further, the nanocomposite exhibits admirable stability with low-level detection of glucose in aqueous media (50 nM glucose) by using a very low concentration of GOx (62 μg in 1 mL).

No abstract

Room temperature ionic liquids (RTILs) are the most common electrolyte now a day, which is usually a molten salt comprised of cationic and anionic charge, generate a neutral species having high thermal stability and exceptional chemical property. Due to these unique properties, RTILs had been used for many applications as a solvent/electrolyte for decades. There are many RTILs, which possess good conductivity, as well as an optimum electrochemical window, which, is suitable for electrochemical sensor application. Among various electrochemical sensors available in the market, the electrochemical gas sensor is a popular device for environmental monitoring. The use of RTILs to the existing technology leads us to new era of sensing where we can able to address sensitivity, stability, robustness, and ability to do multiplex array along with the fundamental behind the electrochemical gas sensor. This paper is consisted of the electrical and electrochemical properties of some popular RTILs along with its application in electrochemical sensing, with a special focus on the electrochemical gas sensor. This review will help the general audience to fabricate the next-gen electrochemical sensor using RTILs.

No abstract

No abstract

Breathomics is a widely emerging tool for noninvasive disease diagnosis and focuses on the detection of various levels of volatile organic compounds and inorganic gases present in human breath. One of the rapid, easy-to-use, and noninvasive detection methods being investigated is a system that can measure exhaled breath ammonia levels and can be correlated to the functional state of protein metabolic pathways and the renal functioning system. In this work, we have demonstrated the development of an electrochemical nose system using ferrocene encapsulated into zeolitic imidazole framework, Fc@ ZIF-8, which can be successfully used for the detection of ammonia levels in breath. This is the first report of an electrochemical gas sensor platform that uses a faradaic probe (that is ferrocene) encapsulated into a metal−organic framework cavity used for disease diagnosis by monitoring the levels of the target gas and can be used for breathomics applications. This work demonstrates that low levels of ammonia gas (up to 400 ppb) can be detected with high sensitivity and specificity. The morphological and structural characterization of the novel, synthesized Fc@ZIF-8 nanocomposite has been performed using powder X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared, ultraviolet−visible spectroscopy, and dynamic light scattering. Electrochemical characterization of the material has been performed using a standard glassy carbon electrode, and further application of the material has been shown using the in-house designed and reported spiral electrochemical notification coupled electrode, used for ammonia gas sensing. Cross-reactivity studies have also been performed to demonstrate sensor specificity toward the target gas. We demonstrate the first of its kind electrochemical bifunctional probe platform that can be used for sensing ammonia levels in breath, with high sensitivity and specificity, due to the hybrid material systemzinc-imidazole framework 8 (having excellent physisorption properties) and ferrocene (acting as a redox mediator). We envision that such a sensing system will allow noninvasive and early diagnosis of chronic kidney disease, thus leading to early treatment and a decrease in the mortality rate.

Herein, development of a unique aqueous-solution-based spray drying route is presented for the preparation of novel molybdenum disulfide–reduced graphene oxide (MoS2-rGO) two-dimensional (2D) nanocomposite sheet with homogeneously dispersed 4–8 stacked 5–15 nm MoS2 sheets on rGO. The developed strategy is based on spray drying of an aqueous solution mixture of ammonium heptamolybdate, ammonium carbonate, and thiourea in the presence of suspended GO followed by calcination under H2 environment. The composite exhibit remarkable interaction between rGO and MoS2. The MoS2 contain majority of 1T phase, high density exposed active edge sites as well as strained sulfur vacancies and oxygen incorporated basal plane. In this process, ammonium carbonate takes crucial role and facilitate the formation of smaller sheets with enhanced inter layer spacing and promote the formation 1T phase. The MoS2-rGO composite exhibit excellent electrocatalytic HER activity and showed a current density of 10 mA/cm2 at 168 mV, a Tafel slope as small as 62 mV/dec, > 98% activity retention after 1000 cycles, which are quite high or comparable to that of similar compositions prepare with complicated methods. The developed protocol is simple, cheap and scalable for large-scale production and extendable for other composite materials for diverse applications.

C-reactive protein (CRP) is considered to be an important biomarker associated with many diseases. During any physiological inflammation, the level of CRP reaches its peak at 48 h, whereas its half-life is around 19 h. Hence, the detection of low-level CRP is an important task for the prognostic management of diseases like cancer, stress, metabolic disorders, cardiovascular diseases, and so on. There are various techniques available in the market to detect low-level CRP like ELISA, Western blot, etc. An electrochemical biosensor is one of the important miniaturized platforms which provides sensitivity along with ease of operation. The most important element of an electrochemical biosensor platform is the electrode which, upon functionalization with a probe, captures the selective antibody–antigen interaction and produces a digital signal in the form of potential/current. Optimization of the electrode design can increase the sensitivity of the sensor by 5–10-fold. Herein, we come up with a new sensor design called the spiral electrochemical notification coupled electrode (SENCE) where the working electrode (WE) is concentric in nature, which shows better response than the market-available standard screen-printed electrode. The sensor is thoroughly characterized using a standard Ferro/Ferri couple. The sensing performance of the fabricated platform is also characterized by the detection of standard H2O2 using a diffusion-driven technique, and a low detection limit of 15 µM was achieved. Furthermore, we utilized the platform to detect a low level (100 ng/mL) of CRP in synthetic sweat. The manuscript provides emphasis on the design of a sensor that can offer good sensitivity in electrochemical biosensing applications.