A SiQD-based hydrogel fiber sensor for portable, on-site β-galactosidase detection in serum

β-Galactosidase (β-Gal), a key senescence biomarker, is crucial for early diagnosis and treatment. In this work, a portable fluorescent fiber optic sensor, based on hydrogel technology, has been designed to monitor β-Gal activity. A tapered optical fiber probe was functionalized with green-emitting silicon quantum dots (SiQDs) via in situ hydrogel polymerization. The sensor ingeniously exploits a β-Gal-initiated cascade reaction: the hydrolysis of the substrate by β-Gal releases a reductant, which promotes the conversion of the Cu(II) chelate into its chromogenic Cu(I) counterpart; the resultant Cu(I) species, in turn, quench the fluorescence of SiQDs via an inner-filter effect. This sensor showed a linear response for β-Gal between 2.0 and 15.0 U L⁻¹, achieving an analytical sensitivity threshold of 1.60 U L⁻¹. It exhibited a combination of high sensitivity, excellent selectivity, strong anti-interference capability, facile fabrication and portability. The sensor accurately quantified β-Gal in real serum and urine samples, with reliability confirmed through standard-addition recovery tests. This represents a mobile, highly effective approach for online, ultratrace β-Gal activity detection in biological specimens and opens new avenues for portable biosensor development.