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.

New concepts
We demonstrate a multimodal photomemristive sensing concept that bridges the field of (photo)electrochemical (PEC) sensing and memristive organic electronics. The carbon nitride poly (heptazine imide) (K-PHI) is capable of “traditional” PEC sensing of a wide range of organic analytes and at the same time shows a characteristic bifunctionality of light absorption coupled to photocatalytic reactivity, and charge storage. Using these unique “optoionic” properties, the sensing information (i.e. the stored charge) can be written onto the sensor and read out based on a number of physical quantities such as photovoltage or color change.


This concept allows us to access new functionalities for sensors: memory of the analyte concentration information, tuneable sensitivities and dynamic sensing ranges, as well as a diverse array of readout methods. Due to the facile sensor geometry – either as films or wireless particles – we circumvent conceptual and technical challenges of existing PEC- or memristive sensing concepts. This work underlines how functionalities from different fields (batteries, photocatalysts, memristors, sensors) can be merged to produce information storing devices with novel functionalities. While this concept accelerates the rapidly emerging research field of memristive sensors into a new direction, it also presents a toolkit to facilitate automated electronic signal processing.

4.3. Preparation of the sensor films and suspensions
Thin films of K-PHI nanoparticles were deposited onto FTO substrates (Sigma Aldrich, surface resistivity of 7 Ω cm−2) via dip coating with 400 dips, 100 mm min−1 extraction speed and 120 s drying time at ambient temperature between the dips (ND-R Rotary Dip Coater, Nadetech).