Ultra-rapidand Ultra-sensitive HFQCM-PEC Dual-ModeBiosensing Platform for Enzymatic Activity Assays based on an Ion-TriggeredGelation Strategy

Abstract Current methods for enzymatic activity assays achieve high sensitivity but require a long assay time, restricting their application in rapid clinical diagnostics. Herein, an ultrarapid and ultrasensitive dual-mode biosensing platform was developed by integrating a high-frequency quartz crystal microbalance (HFQCM, 100 MHz) with a photocurrent polarity switching photoelectrochemical (PEC) strategy, based on Cu2+-triggered sodium alginate (SA) gelation. The platform adopted a universal design where caspase-3 served as a model enzyme to demonstrate its analytical performance. First, a magnetic probe, Fe3O4@AuNPs-peptide-[CuO]n, was synthesized. In the presence of caspase-3, the peptide containing a specific sequence of Asp-Glu-Val-Asp (DEVD) was cleaved, resulting in the release of CuO nanoparticles from the above magnetic probe. Subsequently, the CuO nanoparticles were acidolyzed to generate Cu2+, which induced the ultrafast formation of SA gel on the HFQCM Au chip and SA/MWCNTs–hemin composite gel on the SnS2/ITO electrode within 30 s. Such rapid gelation produced a large frequency response in the HFQCM mode due to the drastic viscoelastic change on the QCM sensing surface and resulted in an obvious photocurrent polarity switching in the PEC mode. Thus, caspase-3 activity was assayed ultrarapidly and ultrasensitively: the entire assay process only required 16 min with a linear response range of 1 fg mL–1 to 100 ng mL–1 (detection limit of 0.32 fg mL–1) in HFQCM mode and 10 fg mL–1 to 100 ng mL–1 (detection limit of 2.75 fg mL–1) in PEC mode. This platform is anticipated to serve as a robust tool in bioanalysis through changing the specific biorecognition elements and has great potential in disease early diagnosis and drug discovery.