Reusable Colorimetric Biosensors on Sustainable Silk-Based Platforms

In biosensor development, silk fibroin is advantageous for providing transparent, flexible, chemically/mechanically stable, biocompatible, and sustainable substrates, where the biorecognition element remains functional for long time periods. These properties are employed here in the production of point-of-care biosensors for resource-limited regions, which are able to display glucose levels without the need for external instrumentation. These biosensors are produced by photopatterning silk films doped with the enzymes glucose oxidase and peroxidase and photoelectrochromic molecules from the dithienylethene family acting as colorimetric mediators of the enzymatic reaction. The photopatterning results from the photoisomerization of dithienylethene molecules in the silk film from its initial uncolored opened form to its pink closed one. The photoisomerization is dose-dependent, and colored patterns with increasing color intensities are obtained by increasing either the irradiation time or the light intensity. In the presence of glucose, the enzymatic cascade reaction is activated, and peroxidase selectively returns closed dithienylethene molecules to their initial uncolored state. Color disappearance in the silk film is proportional to glucose concentration and used to distinguish between hypoglycemic (below 4 mM), normoglycemic (4-6 mM), and hyperglycemic levels (above 6 mM) by visual inspection. After the measurement, the biosensor can be regenerated by irradiation with UV light, enabling up to five measurement cycles. The coupling of peroxidase activity to other oxidoreductases opens the possibility to produce long-life reusable smart biosensors for other analytes such as lactate, cholesterol, or ethanol.

Incorporating Photochromic Viologen Derivative to Unprecedentedly Boost UV Sensitivity in Photoelectrochromic Hydrogel

Developing ultraviolet (UV) radiation sensors featuring high sensitivity, ease of operation, and rapid readout is highly desired in diverse fields. However, the strategies to enhance sensitivity of UV detection remain limited particularly for photochromic materials, which show colorimetric response toward UV irradiation. Guided by our initial goal of facilitating easier handling, we formulated a viologen derivative ([H₂L]-SC) incorporating hydrogel-based UV sensor which not only inherits the photochromism of [H₂L]-SC but also engenders an unprecedented reversible photoelectrochromic response that is absent in either [H₂L]-SC or hydrogel alone. Judicious synergy between photochromic [H₂L]-SC and polyacrylamide (PAM) converts the colorimetric response of [H₂L]-SC into the electrical resistance change of [H₂L]-SC@PAM, which amplifies the UV sensitivity of [H₂L]-SC by 2 orders of magnitude. Explicitly, the limit of detection (LOD) for UV decreases from 296.3 mJ/cm² based on the UV-vis absorption spectra of [H₂L]-SC to 2.83 mJ/cm² derived from the resistance variation of [H₂L]-SC@PAM. Moreover, linear correlation between the resistance reduction rate of [H₂L]-SC@PAM and UV dose rate can be established, rendering it as a dual platform for quantifying both the accumulated UV dose and the instant dose rate. In addition, the proposed strategy based on constructing photoelectrochromic hybrids offers a new pathway to boost the UV sensitivity that could be universal for other photochromic materials.