Biosensing with Tailored Track-Etched Nanochannels
Authors: Kaya Dila , Cayón Vanina M. , Trautmann Christina , Toimil Molares Maria Eugenia 
Published: February 2024

Inspired by the high sensitivity, efficiency and selectivity of biological ion channels, the development of solid-state nanochannel sensors has been at the forefront of nanotechnology research in the last years. Many researchers worldwide have concentrated their efforts on the development of artificial nanochannels that can mimic the features of biological ion channels. These synthetic nanostructures are based on abiotic materials which provide higher robustness, thermal stability, chemical versatility and mechanical resistance than their biological counterparts. Furthermore, synthetic nanochannels and specific surface functionalization strategies have enabled fine control over the geometry and charge distribution which yielded the ability to manipulate the flux of ions through the channel. This gave rise to the formation of nanochannel-based platforms with applications in (bio)sensing as well as other fields. The development of chemical- and biosensors requires a combination of reliable nanofabrication techniques and versatile surface modification strategies, which render high sensitivity and high selectivity, respectively [1].
Tailored single polymer nanochannels are routinely fabricated by ion-track nanotechnology. Polymer films are first irradiated with individual swift heavy ions at the GSI UNILAC accelerator. Each ion generates a highly localized cylindrical damage zone along its trajectory. These so-called ion tracks are subsequently dissolved and enlarged in a chemical etching process. By selecting suitable etching conditions, geometry (cylindrical, conical or bullet-like) and size of the nanochannels can be adjusted. The nanochannel surface can then be functionalized by means of different chemical strategies to enhance the sensing capabilities.
There are two main nanochannel sensing techniques, ion current rectification (ICR) and resistive-pulse sensing (RPS). Both are affected by the geometry and surface charge of the nanochannel and based on measuring the change in ion current flowing through the channel induced by the chosen analyte [2]. In both approaches, the presence of a target analyte triggers a variation in the physicochemical properties of the channel which can be related to measurable changes in the transmembrane current, and is proportional to the analyte concentration.
In this contribution, we will present nanochannel sensing platforms based on several single polymer channels fabricated by ion-track nanotechnology and a selection of surface functionalization strategies applied to the nanochannels. We will then discuss selected examples recently obtained with these tailored functionalized nanochannels and demonstrate selective and sensitive sensing applications based on both the ICR and RPS phenomena.
[1] Toum Terrones, Y., Cayón, V. M., Laucirica, G., Cortez, M. L., Toimil-Molares, M. E., Trautmann, C., ... & Azzaroni, O. (2022). Ion Track-Based Nanofluidic Biosensors. In Miniaturized Biosensing Devices: Fabrication and Applications (pp. 57-81). Singapore: Springer Nature Singapore.
[2] Kaya, D., & Keçeci, K. (2020). Track-etched nanoporous polymer membranes as sensors: A review. Journal of The Electrochemical Society, 167(3), 037543.