A gate-induced insulating behavior at zero magnetic field is observed in a high-mobility suspended monolayer graphene near the charge neutrality point. The graphene device initially cleaned by a current annealing technique underwent a thermopressure cycle to allow short-range impurities to be adsorbed directly by the ultraclean graphene surface. The adsorption process generated a strong temperature- and electric-field-dependent behavior on the conductance of the graphene device. The conductance around the neutrality point is observed to be reduced from around $e^2/h$ at 30 K to $\sim 0.01e^2/h$ at 20 mK. A direct transition from an insulator to a quantum Hall conductor within $\approx 0.4\text{T}$ accompanied by broken-symmetry-induced $\nu =0,\pm 1$ plateaus confirms the presence of intervalley scatterers.

We present a flexible pH sensor which leverages the unique properties of reduced graphene oxide/polyaniline (rGO/PANI) composite films through an efficient and scalable hybrid microfabrication approach, wherein the rGO/PANI films are conformally coated on flexible polyethylene terephthalate (PET) substrates via dip-coating and thereafter lithographically patterned into precise arrays of interdigitated electrodes (IDEs), serving both as the pH-active medium and the electrical interface. Upon dip-coating, a thermal reduction process is performed to yield uniform rGO/PANI composite layers on PET substrates, where the PANI content is adjusted to 20% to optimize conductivity and protonation-driven response. Composition optimization is first performed using inkjet-printed silver (Ag) contacts and a conductometric readout mechanism is employed to explore pH-dependent behavior. Subsequently, IDE arrays are defined in the rGO/PANI using photolithography and oxygen-plasma etching, demonstrating clean pattern transfer and dimensional control on flexible substrates. Eliminating separate contact metals in the final design simplifies the stack and reduces cost. A set of IDE geometries is evaluated through I–V measurements in buffers of different pH values, revealing a consistent, monotonic change in electrical characteristics with pH and geometry-tunable response. The present study demonstrated that the most precise pH measurement was achieved with an 80:20 rGO/PANI composition within the pH 2–10 range. These results establish rGO/PANI IDEs as a scalable route to low-cost, miniaturized, and mechanically compliant pH sensors for field and in-line monitoring applications.

Nucleic acid-based biosensor technologies are useful to precisely detect genetic footprints at low concentrations with high specificity and selectivity. They commonly rely on incorporating nucleic acid probes onto optical, electrochemical, or electrical transducers. Among various sensing modalities, approaches based on direct electrical measurements offer advantages in label-free detection, portability for point-of-care analysis, and direct integration with electronic readout circuits facilitating data processing, transfer and remote interpretation. In this work, we demonstrate a novel fabrication approach which couples conventional optical lithography and oxygen plasma-based etching with high-resolution electron-beam lithography to rapidly pattern poly(methyl methacrylate) (PMMA) e-beam resist at varying feature sizes (i.e. both large and small device areas), which would otherwise require extremely long exposure durations up to days with standalone e-beam lithography. This allows the fabrication of realistic biosensor chips in arrayed format, co-integrating millimeter (mm)-scale electrical peripherals and nanoscale (nm) sensing elements utilizing a simple and high-throughput process. The feasibility of the approach is demonstrated by successful immobilization of thiol-functionalized peptide nucleic acid (PNA) probes on ~ 60 nm-wide gold nanowires (AuNWs) integrated with a PDMS microchannel. Fabrication of biochips, integration with microfluidics and self-assembly of PNA probes are characterized by optical microscope imaging, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS).