Tyndall Effect Enables Highly Sensitive Colorimetric Detection of a Variety of Analytes

This work initially reports the use of a quite familiar optical phenomenon of colloidal solutions, namely the Tyndall Effect (TE) as signal readout for highly sensitive colorimetric chemical and biological analysis. Taking gold nanoparticles (GNPs) as a model colloid, the TE-inspired assay (TEA) is developed based on the conversion of a specific recognition event (e.g., the aptamer-analyte binding) into the aggregation of GNPs leading to a significant TE enhancement. In the TEA, a cheap laser pointer pen is used as a handheld light source, while a smartphone serves as a portable quantitative reader. The results show that the TE signaling strategy achieves a ~1000-fold sensitivity improvement compared with the most common surface plasmon resonance signaling method using GNPs. The utility of the TEA is well demonstrated with the inexpensive, rapid, and portable detection of trace levels of analytes ranging from an important small-molecule drug (cocaine, ~1.5 pM detection limit) to a protein biomarker (inter...