  We report the charge storing 2D carbon nitride potassium poly(heptazine
imide), K-PHI, as a direct memristive (bio)sensing platform. Memristive devices
have the potential to innovate current (bio)electronic systems such as
photo-electrochemical sensors by incorporating new sensing capabilities
including non-invasive, wireless remote and time-delayed (memory) readout. We
demonstrate a direct photomemristive sensing platform that capitalizes on K
PHI's visible light bandgap, large oxidation potential and intrinsic optoionic
light energy storage properties. Our system simultaneously enables analyte
concentration information storage as well as potentiometric, impedimetric and
coulo-metric readouts on the same material, with no additional reagents
required. Utilizing the light-induced charge storage function of K-PHI, we
demonstrate analyte sensing via charge accumulation and present various methods
to write/erase this information from the material. Additionally, fully wireless
colorimetric and fluorometric detection of the charged state of K-PHI is
demonstrated and could facilitate its use as particle-based in-situ sensing
probe. The various readout options of the K PHI's response enable us to adapt
the sensitivities and dynamic ranges without modifying the sensor. We
demonstrate these features using glucose as an example analyte over a wide
range of concentrations (50 $\mu$M to 50 mM). Moreover, due to the strong
oxidative power of K-PHI, this sensing platform is able to detect a large
variety of organic or biologically relevant analytes. Since PHI is easily
synthesized, based on earth abundant precursors, biocompatible, chemically
robust and responsive to visible light, we anticipate that the sensing platform
presented herein opens up novel memristive and neuromorphic functions.
