First project: Fabrication of GO-modified multiplexed wax-on-plastic chip for electrochemical detection of nucleic acids. (Completed)

Multiplex biosensing chips are in high demand for simultaneous detection of biomarkers with reduced sample quantity and analysis costs. Wax-on-plastic platforms represent a new class of flexible devices, that can be fabricated in a variety of formats, including microwells, microfluidic channels, and electrochemical systems. Here, we present the fabrication of the first multiplexed wax-on-plastic electrochemical chip with eight working electrodes modified with graphene-oxide (GO) nanosheets. The fabrication procedure involves printing a device pattern on PET (Polyethylene terephthalate) substrate using a Xerox ColorQube printer, followed by inkjet printing (EPSON, ET-M1170) of a conductive layer of silver nanoparticles (AgNPs) in the hydrophilic islands of the substrate.

The GO-modified working electrodes were employed for nucleic acid detection without the covalent immobilization of a probe. Specifically, the peptide nucleic acid (PNA) probe (CTG-6) was adsorbed on the GO surface in a concentration range of 100 pM – 100 nM. The (Differential Pulse Voltammetry) peak current of the PNA-modified electrodes was found to be higher than its background in the presence of 1 mM Fe(CN)63-/4- prepared in phosphate buffer solution. P. K. Das, O. Adil, and M. H. Shamsi*, “First multiplexed electrochemical wax-on-plastic chip: PNA/GO interface integration for DNA detection”, J. Micromech. Microeng. 2023,33,097001 (7pp).

Second project: pseudodouridine-modified RNA probe for label-free electrochemical biosensing. (Completed)

Pseudouridylation, a conversion of uridine to pseudouridine (Y) within an RNA chain, is one of the most common modifications in nature. Pseudouridine provides structural stability to RNA and is significant for the modulation of RNA’s conformational dynamics. RNA has been rarely employed as a probe for biosensing because of its susceptibility to enzymatic degradation and its tedious handling. To explore its potential as a biosensing probe, we explored the first pseudouridine-modified RNA probe (Y-RNA). We took advantage of the natural affinity between nucleic acids and molybdenum disulfide (MoS2) due to the van der Waals force interaction between the nucleobases of RNA and the basal plane of the MoS2. The Y-RNA probe was adsorbed on the MoS2 surface before being exposed it to DNA and RNA targets. The probe modification and hybridization of a target on the biosensing platform significantly reduce the interfacial resistance of MoS2 electrodes in the presence of a soluble redox probe, which was used as a readout for detection. The change in resistance (%ΔRCT) (Electrochemical Impedance Spectroscopy) was calculated based on the resistances of unmodified and modified MoS2 electrodes. We anticipate that Y-RNA may replace DNA-based biosensing in the future. P. K. Das, A. P. Degregorio, O. Adil, M. Sumita, and M. H. Shamsi*, “Pseudouridine-modified RNA probe for label-free electrochemical biosensing”, Analyst, 2024,149, 1310-1317.

Review Article: Published ( P. K. Das, O. Adil, and M. H. Shamsi*, ACS Applied Nano Materials - Electrochemical Biosensing Based on Nucleic Acid Adsorption on Two-Dimensional Nanomaterials: A Review. ACS Appl. Nano Mater. 2025, 8, 14, 6797–6817) .

Third project: Charge transfer study of DNA/MoS2 interface. (NIH Funded)

Molybdenum disulfide (MoS2) is a transition metal dichalcogenide, which has recently become popular for biosensing applications due to its large band gap. Theory predicts that MoS2 has differential adsorption affinity for nucleic acids via van der Waals interactions between the aromatic rings of nucleobases and the basal plane of MoS2. Further, these interactions tend to reduce the band gap of MoS2 improving charge transfer through the interface. Such sequence-dependent improvement in the electronic property may help develop a MoS2-based sequencing technology that might not require a label and covalent immobilization of a probe. The resistance of the study was calculated through electrochemical impedance spectroscopy (EIS). (Published manuscript Charge Transfer Study of Artificial Nucleic Acid/MoS2 Interface for Nucleic Acid Detection"Prabhangshu K. Das, Mohammad A. Asad, William Almy, Anne Casebeer, Mohtashim H. Shamsi*.https://doi.org/10.1021/acsanm.5c01841 .

Ongoing project: Synthesizing of molybdenum disulfide quantum dots for fabrication of electrochemical microfluidic devices and investigation as electrocatalysts.

Aim-1: Optimization channel of microfluidics, microfluidics device design, and fabrication, MoS2QD synthesis using liquid exfoliation method.

Aim-2: Characterize the formulation of MoS2QD ink, modify devices using the ink, and characterize them through UV-Vis, TEM, SEM, EDX, AFM, and electrochemical techniques (cyclic voltammetry and differential pulse voltammetry).

Aim-3: Probe optimization, blocking agent studies, and target detection with specific studies.

MoS2 quantum dots

Ongoing project: Electrografted carboxylate functionalization of MoS2 using as an electrocatalyst and biosensor.

Aim -1: Carboxylate functionalization of MoS2 using electrografted technique, and characterization (AFM, SEM, EDX, Raman, FTIR, and electrochemical)

Aim-2: Investigation on electrocatalyst of MoS2-COOH using two electrolytes, H2SO4, and KOH ( Polarization technique)

Aim -2: MOS2-COOH using as a modifier for electrochemical biosensor platform fabrication.