Magnetically Controlled Photothermal, Colorimetric, and Fluorescence Trimode Assay for Gastric Cancer Exosomes Based on Acid-Induced Decomposition of CP/Mn-PBA DSNBs

The accurate quantification of cancer-derived exosomes, which are emerging as promising noninvasive biomarkers for liquid biopsies in the early diagnosis of cancer, is becoming increasingly imperative. In our work, we developed a magnetically controlled photothermal, colorimetric, and fluorescence trimode aptasensor for human gastric cancer cell (SGC-7901)-derived exosomes. This sensor relied on CP/Mn-PBA DSNBs nanocomposites, created by decorating copper peroxide (CP) nanodots on polyethyleneimine-modified manganese-containing Prussian blue analogues double-shelled nanoboxes (PEI-Mn-PBA DSNBs). Through self-assembly, we attached CD63 aptamer-labeled CP/Mn-PBA DSNBs (Apt-CP/Mn-PBA DSNBs) to complementary DNA-labeled magnetic beads (cDNA-MB). During exosome incubation, these aptamers preferentially formed complexes with exosomes, and we efficiently removed the released CP/Mn-PBA DSNBs by using magnetic separation. The CP/Mn-PBA DSNBs exhibited high photoreactivity and photothermal conversion efficiency under near-infrared (NIR) light, leading to temperature variations under 808 nm irradiation, correlating with different exosome concentrations. Additionally, colorimetric detection was achieved by monitoring the color change in a 3,3',5,5'-tetramethylbenzidine (TMB) system, facilitated by PEI modification, NIR-enhanced peroxidase-like activity of CP/Mn-PBA DSNBs and their capacity to generate Cu²⁺ and H₂O₂ under acidic conditions. Moreover, in the presence of Cu²⁺ and ascorbic acid (AA), DNA sequences could form dsDNA-templated copper nanoparticles (CuNPs), which emitted strong fluorescence at around 575 nm. Increasing exosome concentrations correlated with decreases in temperature, absorbance, and fluorescence intensity. This trimode biosensor demonstrated satisfactory ability in differentiating gastric cancer patients from healthy individuals using human serum samples.