Intelligent Visualization of Single Microbead Bubbling Enables Attomolar Protein Quantification

Quantification of low-abundance proteins in biofluids using affordable and portable biosensors stands as the top priority for point-of-care testing and in-field disease screening/monitoring. Herein, we propose a cellphone-based portable immunoassay platform coupled with an intelligent single microbead (SMB) bubbling visualization mechanism, which allows for facile, low-cost, and highly sensitive protein analysis. The use of solely an SMB as the immunocarrier can remarkably boost the sensitivity by superenriching the target-mediated, platinum nanoparticle (PtNP)-involved immunocomplexes on its surface. As such, even trace amounts of target proteins can bring highly gathered PtNPs on the SMB, which rapidly catalyze the production of noticeable and highly centralized oxygen (O₂) bubbles firmly adhered to the SMB in just 50 s. The SMB bubbles can be facilely captured and imaged by a cellphone-attached lens, and the area of bubbles is employed as a novel signal readout mode for the ultrasensitive analysis of proteins down to the aM levels. Assisted by a self-written image analysis algorithm, the SMB-bubble imaging, recognition, area calculation, and target qualification are all automatically streamlined into an all-in-one cellphone application (App), achieving simple yet sensitive protein detection. This proposed intelligent platform provides a highly sensitive and cost-effective substitute for critical biomarker testing and paves a new way for cellphone-enabled portable biosensing.