Ultrasensitive Electrochemical Immunoassay Based on Cargo Release from Nanosized PbS Colloidosomes

Colloidosome is a novel nanostructure composed of millions of colloid particles. In this work, nanosized PbS colloidosomes were initially prepared and applied as nanoprobes for an ultrasensitive immunoassay. The colloidosomes were simply prepared in mild conditions by assembling the elementary approximately 8 nm PbS nanoparticles at the water-in-oil interface of emulsion droplets. To enhance the rigidity and biocompatibility of the colloidosomes, interfacial polymer was introduced by utilizing self-polymerization of dopamine. By treating with dilute nitric acid, a bursting release of lead ions from the colloidosomes occurred and the lead ions can be detected easily by anodic stripping voltammetry. In this way, a colloidosome-based electrochemical immunoassay was developed by using the nanosized PbS colloidosomes as electroactive labels. The proposed method featured a linear calibration range from 10 fg·mL^-1 to 100 ng·mL^-1 with a low detection limit of 3.4 fg·mL^-1 for the detection of human epididymis protein 4. This work introduced a new member for the family of colloidosomes and offered a novel perspective for the rational implementation of various colloidosomes for novel low-abundance cancer biomarkers analysis.