Bile acid-based receptors and their applications in recognition

Ion recognition has attracted great attention in the past decades because of its important role in biology, medicine, environment, and chemistry. The combination of rigidity, curved structure and amphiphilic nature makes bile acids a host system for ion recognition. In addition, the availability of hydroxyl groups in bile acids can be used for further derivatization to develop various ion recognition receptors. The detection of ions is revealed by the binding constant k_a value, log approach, and UV-visible or ¹H NMR titration, while visual detection is determined by gel-phase transition, colorimetric and fluorescent probes. In this review, we have discussed the bile acid-based receptors and their ion-recognition capability. These bile acid-based systems have the potential for the development of anion transport for biological activity.

Highly Selective Detection of Iodide in Biological, Food, and Environmental Samples Using Polymer-Capped Silver Nanoparticles: Preparation of a Paper-Based Testing Kit for On-Site Monitoring

This work describes a facile synthesis of polymer-capped silver nanoparticles at room temperature. Chitosan oligosaccharide lactate-capped silver nanoparticles (COL-AgNPs) show the surface plasma resonance (SPR) band at 400 nm. The color of the COL-AgNPs was observed to be brownish yellow. The synthesized COL-AgNPs are stable for 5 months. The COL-AgNPs were characterized by UV-vis, X-ray diffraction, high-resolution transmission electron microscopy (HR-TEM), mass, and Fourier transform infrared spectral techniques. The obtained COL-AgNPs are monodispersed, and the range of the particle diameter was calculated to be 16.37 ± 0.15 nm by HR-TEM. We have utilized the COL-AgNPs as a probe to sense iodide (I^-). The SPR band of COL-AgNPs was decreased after the addition of iodide, and the color of the solution changed to colorless. Based on the decreases in SPR band absorbance, the concentration of iodide was calculated. The detection limit was found to be 108.5 × 10^-9 M (S/N = 3). Other interferences (825- and 405-fold) did not interfere with the detection of 1.48 × 10^-6 M iodide. The sensing mechanism was also discussed. Finally, we have successfully applied our sensing system for the detection of iodide in tap water, river water, pond water, blood serum, urine, and food samples. Good recoveries are obtained with spiked iodide in the real samples. Importantly, we have developed a paper-based kit using wax-printed paper for the on-site monitoring of iodide. The developed paper-based kit absorbance was validated with the microplate reader. To the best of our knowledge, this is the first report that used six different real samples for the detection of iodide and development of the paper-based kit for on-site monitoring.

Facile method for iodide ion detection via the fluorescence decrease of dihydrolipoic acid/beta-cyclodextrin protected Ag nanoclusters

In this work, novel photoluminescent Ag nanoclusters (Ag NCs) with red emission are synthesized and successfully used for detecting iodide ion (I^-). The dihydrolipoic acid (DHLA) is used as the stabilizing agent and beta-cyclodextrin (β-CD) is used as the auxiliary stabilizing agent. DHLA and β-CD are combined with Ag atoms by the formation of AgS bonds and hydrophobic interaction, respectively. Functionalization of β-CD endows good photoluminescent properties and solubility in water to the Ag NCs. The obtained DHLA and β-CD-protected Ag NCs (DHLA/β-CD-Ag NCs) are spherical and display a dispersed state. However, the DHLA/β-CD-Ag NCs are aggregated in the presence of I^-, accompanied by the decrease in their fluorescence intensity. Because the integrity of β-CD cavities is retained on the surface of DHLA/β-CD-Ag NCs, which preserves their capability for I^- host-guest recognition, the DHLA/β-CD-Ag NCs combine with I^- through the formation of inclusion complexes. Based on this phenomenon, the prepared DHLA/β-CD-Ag NCs can be designed as a novel fluorescent probe for I^- detection. The limit of detection (LOD) is calculated as 0.06 μM, indicating that it is an ideal probe for I^- detection in practical applications.

A rhodamine-based sensor for Hg2+ and resultant complex as a fluorescence sensor for I−

A rhodamine-based sensor displays a quick response for Hg²⁺. The resulting complex can act as a reversible fluorescence sensor for I⁻.