Highly Sensitive Colorimetric Detection of a Variety of Analytes via the Tyndall Effect

Abstract

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 hand-held 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 (interferon-γ, ∼2.2 fM detection limit) and a toxic metal ion (Ag+, ∼1.4 nM detection limit). In addition, as the TE enhancement simply stems from the aggregation of either bare (unmodified) or modified GNPs, the TEA is universally applicable to almost all of the existing GNP-based liquid-phase colorimetric assays. The TEA method developed herein lights a new way for equipment-free point-of-care analysis in various fields including medical diagnosis, food safety evaluation, and environmental monitoring, especially in the resource-poor areas of the world.

Self-Assembled Copper Polypyridyl Supramolecular Metallopolymer Achieving Enhanced Anticancer Efficacy

“…Tyndall effect was observed in the solution of [CuCl(pip) 2 ]Cl in proton solvent CH 3 CH 2 OH/H 2 O (Figure 6), indicating the formation of self-assembled species [46], while no Tyndall phenomenon observed in aprotic solvent DMF. Therefore, the presence of proton solvent could be a determining factor for the self-assembly, as proton solvent could provide H atom feasible for the aggregation driven by hydrogen bond.…”

Operando laser scattering: probing the evolution of local pH gradients on complex electrode architectures

“…Overall, the presented operando TE-based approach constitutes a signi cant progress in analytical strategies aiming at investigating the dynamics of the interfacial double layer because it provides instantaneous extended pH read-out on surfaces with distinct local reactivities and unique spatiotemporal resolution only limited by the acquisition capabilities of the employed camera (here 30 three-dimensional reactivity maps per second). Besides straightforwardly enabling comparative reaction kinetics intrinsic to complex electrode architectures, the approach is also amenable to quanti cation and exhibits outstanding sensitivity 28 . Finally, its applicability can be universally extended to any other nanoaggregation/decomplexation process of interest (e.g., electrocoagulation, mineral removal and separation, electrosynthesis, among others) occurring at light-addressable interfaces provided the probed colloids are smaller than the wavelength of visible light.…”

“…This phenomenon has already been used as a visual screening method to detect microprecipitates in blends of parental drug solutions 22,23 as well as to evaluate nanolevel aggregation and characterise colloidal catalyst and functional materials [24][25][26][27] . More recently, Xiao et al 28 added quantitative character to a TE-based colorimetry approach and demonstrated a ca. 1000-fold sensitivity improvement compared to common surface plasmon resonance-based techniques.…”

On-site, rapid and visual method for nanomolar Hg2+ detection based on the thymine–Hg2+–thymine triggered “double” aggregation of Au nanoparticles enhancing the Tyndall effect

“…More recently, another powerful optical property of the colloidal metal nanoparticles like the AuNPs-Tyndall effect (TE)-has been explored for enhanced colorimetric signaling. [25][26][27] The TE, which is named for the 19th-century British physicist John Tyndall, is dened as the bright "pathway" formed when a light beam passes a colloidal solution due to the scattering effect of the colloidal particles on the light. 28,29 Its intensity positively relies on both of the particle size and concentration.…”

“…However, the previous AuNP-based TEAs still suffer from the disadvantages of multi-step nanoprobe modication, relatively tedious analytical time ($1 h), and/or more ideal assay specicity remains a big challenge. 25,26 With these insights, herein we initially describe the proof-ofconcept of a new TEA method that combines the unmodied (bare) AuNPs with functional nucleic acids for the rapid, highly specic visual detection and quantication of Hg 2+ ions at nM levels. Considerable studies have proven that the thymine-rich single-stranded DNA (ssDNA) possesses an excellent selective binding affinity to Hg 2+ .…”