Photomemristive sensing via charge storage in 2D carbon nitrides

Photomemristive sensors have the potential to innovate current photo-electrochemical sensors by incorporating new sensing capabilities including non-invasive, wireless and time-delayed (memory) readout. Here we report the charge storing 2D carbon nitride potassium poly(heptazine imide), K-PHI, as a direct photomemristive sensing platform by capitalizing on K-PHI's visible light bandgap, large oxidation potential, and intrinsic optoionic charge storage properties. Utilizing the light-induced charge storage function of K-PHI nanosheets, we demonstrate memory sensing via charge accumulation and present potentiometric, impedimetric and coulometric readouts to write/erase this information from the material, with no additional reagents required. Additionally, wireless colorimetric and fluorometric detection of the charging state of K-PHI nanoparticles is demonstrated, enabling the material's use as particle-based autonomous sensing probe in situ. The various readout options of K-PHI's response enable us to adapt the sensitivities and dynamic ranges without modifying the sensing platform, which is demonstrated using glucose as a model analyte over a wide range of concentrations (50 μM to 50 mM). Since K-PHI is earth abundant, biocompatible, chemically robust and responsive to visible light, we anticipate that the photomemristive sensing platform presented herein opens up memristive and neuromorphic functions.

Tunable Switching Behavior of GO-Based Memristors Using Thermal Reduction

This work reports on the fabrication of a novel planar reduced graphene oxide (rGO) memristor (MR) device. For the first time in the literature, the MR tunable resistive switching behavior is controlled by the GO reduction time at a constant temperature. The device is fabricated using standard microfabrication techniques on a flexible cyclic olefin copolymer substrate (COC). Thermal reduction of the GO layer at low temperatures (100 °C) avoids the drawbacks of chemical reduction methods such as toxicity and electrode metal damage during fabrication, while allowing for fine-tuning of the MR’s switching behavior. The device has analog switching characteristics, with a range of different resistance states. By taking advantage of the slow nature of GO thermal annealing, the switching properties of the rGO memristors can be precisely controlled by adjusting the reduction period. At short annealing times (i.e., T < 20 h), the devices switch from high to low resistance states, while at longer annealing times the switching behavior is reversed, with the device switching from low to high resistance states (LRS to HRS). Resistive switching occurs as a result of the diffusion and removal of the oxygen functional groups in the GO film caused by Joule heating induced by the electric current. Complete electrical characterization tests are presented along with wettability and X-ray diffraction (XRD) tests. This work opens a new vision for realizing rGO-based MR devices with tunable switching properties, broadening the application horizon of the device.

Nanowire Sensors in Cancer

In 2006, the group of Dr C.M. Lieber pioneered the field of nanowire sensors by fabricating devices for the ultra-sensitive label-free detection of biological macromolecules. Since then, nanowire sensors have demonstrated their ability to detect cancer-associated analytes in peripheral blood, tumor tissue, and the exhaled breath of cancer patients. These innovative developments have marked a new era with unprecedented detection performance, capable of addressing crucial needs such as cancer diagnosis and monitoring disease progression and patient response to therapy. The ability of nanowire sensors to identify molecular features of patient tumor represents a first step toward precision medicine, and their integration into portable devices has the potential to revolutionize cancer diagnosis and patient monitoring.