Coordination-driven reversible supramolecular assembly formation at biological pH: Trace-level detection of Hg2+ and I- ions in real life samples

A dual-signaling surface-enhanced Raman spectroscopy ratiometric strategy for ultrasensitive Hg2+ detection based on Au@Ag/COF composites

Heavy metal ion pollution poses significant risks to human health and ecological systems, and its monitoring is important. A sensitive and accurate surface-enhanced Raman spectroscopy (SERS) detection assay for Hg2+ was developed using Au@Ag/COF substrates and Y-shaped DNA labeled with two Raman reporters. The Au@Ag NPs in the COF produced robust and uniform E-fields, improving their detection reproducibility. The Y-shaped DNA design increased sensitivity with a low detection limit of 5.0 × 10-16 M by bringing the Raman reporter closer to the substrate surface. Additionally, the use of two Raman reporters allowed for a ratiometric method, improving detection accuracy by detecting both "signal-off" and "signal-on" signals. This selective sensor exhibited excellent recovery in river water, tap water, and milk samples, showcasing its robust biosensing capability for the detection of Hg2+ and its potential for sensing other heavy-metal ions in food and environmental applications.

Label-free multimodal analysis of copper ions at below permissible exposure limit in the aqueous medium

An anthraimidazoledione based amphiphilic dye molecule was synthesized that shows formation of tuneable charge-transfer state in solution, susceptible to change in pH, polarity and hydrogen bonding ability of the medium. The compound also showed formation of nanoscopic self-assembled structure in water medium. The probe molecule can achieve multimodal detection (colorimetric, fluorimetric and electrochemical) of copper ions as low as 0.3 ppm in the aqueous medium. Addition of copper leads to dose-dependent ratiometric change in solution color from yellow to purple. The mechanistic investigation indicates that the coordination of copper ions was possible via simultaneous engagement of both imidazole nitrogen ends and neighbouring hydroxyl unit. Not only optical property, the changes in microenvironment also influence the selectivity as well as sensitivity of the probe molecule towards Cu2+ ions. Further, the optical probe is used for detection as well as quantification of copper ions in natural water samples without any sample pretreatment. Low-cost, reusable paper strips are developed for rapid, on-location detection of residual Cu2+ in real-life samples.

Dye-surfactant co-assembly as the chromogenic indicator for nanomolar level detection of Cu(I) ions via a color-changing response

Polyaromatic amphiphilic probes have been developed, that can be involved in chromogenic detection of Cu⁺ ions in anionic micelles. A rapid change in solution color from yellow to orange was observed in the presence of Cu⁺ ions. The detection limit was found at the nanomolar range. To the best of our knowledge, this is the first report of the visible detection of Cu⁺ ions in aqueous medium using anionic micelles as a stabilizing agent. Interestingly, the compound can also detect Cu⁺ ions, generated in situ from physiological redox processes. The mechanistic investigation suggests that the probe molecule forms a diamagnetic tetrahedral complex with the Cu⁺ ion, coordinating through a pyridyl ketone unit. In addition, we have also followed the interaction with Cu⁺ on a bilayer surface made of anionic phospholipids. Further, a Cu²⁺-probe ensemble is used to assay the reducing ability of different biogenic thiols depending upon the pK_a of their sulfhydryl (-SH) group. This allows us to determine the amount of reducing thiols present in human urine samples. Considering the high sensitivity of the present system, we screened water samples collected from different natural sources for Cu⁺ ions. Nearly 100% recovery values with considerably small relative standard deviations (<5%) indicate that the present system is indeed suitable for real-life sample analysis. Finally, low-cost, reusable, chemically-modified paper strips have been developed for rapid, on-location detection of Cu⁺ ions.

Ppb-Level, Dual Channel Sensing of Cyanide and Bisulfate Ions in Aqueous Medium: Computational Rationalization of Ion-Dependent ICT Mechanism

In this report, three oxidized diindolylarylmethane (DIAM) based chromogenic probes (designated as 1, 2, and 3) have been developed for the simultaneous and dual-channel detection of cyanide (LOD: 6.2 ppb)...