Research Projects

Biological ion channels have inspired researchers to fabricate biomimetic synthetic nanopores for ion pumps, nano-gating, energy conversion, and biosensing. Nanopore sensors are gaining traction for amplification-free, label-free, and high-throughput detection capabilities. Ionic selectivity in nanopores leads to the development of ion concentration polarization (CP) zones at the entrance and exit regions, under external electric fields. Asymmetric enrichment and depletion zones develop due to non-uniformity in shape (conical or funnel-shaped), surface charge (bi-polar), or lopsided buffer strengths under opposite voltage polarities. This causes ionic current rectification (ICR) and subsequent diode-like characteristics of nanopores. In ICR-based sensing strategies, the sensitivity of detection depends on the ICR ratio, Q=|I(-Vex)/I(-Vex) |, where I(+Vex ) and I(-Vex ) denote the currents at +Vex and -Vex, respectively. High Q values are desirable for accurate detection but have proven difficult to achieve due to challenges associated with nanofabrication and functionalization of the pores. In addition, high rectification ratios are typically achieved when the size of at least one pore mouth is near the Debye length, with diminished effects in pores exceeding ten times this scale. The thermophoresis of dissolved ions induces thermoelectricity in liquid electrolytes according to the Soret effect (ionic counterpart of the Seebeck effect). In charged nanopores/nanochannels filled with an electrolyte, an axial temperature gradient leads to the development of a non-uniform EDL which induces a thermal voltage (Vth), in tandem with the Soret effect. Thus, it is intuitive that there would be ICR on the application of an external electric field under non-isothermal conditions. Interestingly, some of the preliminary studies by our group at IIT (BHU) Varanasi, indicate that Q values exhibited by the nanofluidic diode vary significantly with ±Vex and pH of the electrolyte. At higher voltages, the temperature-dependent characteristics of the enrichment and depletion layers dictate the ICR ability of the diode. This project aims to leverage the temperature-gradient-induced modification of the CP zones to fabricate current rectifying nano/microfluidic diodes. The project also aims to utilize the thermally rectifying diodes to develop an integrated all-in-one biosensing platform, with a particular focus on the detection of biomarkers associated with cardiovascular diseases and breast cancer. The biggest advantage of the proposed strategy is that it can work with uniform pores/channels, which otherwise do not exhibit ICR. The proposed strategy is anticipated to (a) eliminate or reduce geometry or surface modification of the nanopores/nanochannels, (b) induce ICR even in large-diameter (micron-sized) pores, (c) enable label-free, enhanced detection of low-abundance analytes, and (d) easily combine with other methods to give synergistic effects.

Thermal-gradient, concentration polarization, ionic-current-rectification, iontronics, micro/nanofluidics, biosensing