Highly selective and sensitive fluorescent chemosensor for femtomolar detection of silver ion in aqueous medium

The ratiometric fluorescent sensor based on the mixture of CdTe quantum dots and graphene quantum dots for quantitative analysis of silver in drinks

Silver nanoparticles can be used in antibacterial packaging or disinfection. Research has shown that sugary fluid induces the leaching of silver nanoparticles into water, which may be harmful to humans. Single wavelength fluorescence analysis has been used for quantitative analysis of silver nanoparticles but suffers from low specificity and poor anti-interference ability. In this paper, a ratiometric fluorescence sensor system (GCS) was used for the detection of Ag+, which realized both visual detection and quantitative analysis of silver in drinks. The color changes of GCS with different concentrations of Ag+ are distinguishable and easy to analyze. There is also a good linear relationship between the concentrations of Ag+ and varieties of F424 nm/F570 nm, and the lowest detection limit reached 0.2266 nmol/L. This GCS shows good selectivity and recovery and could be used for the detection of Ag+ in drink samples.

Horseradish Peroxidase-Encapsulated Fluorescent Bio-Nanoparticle for Ultra-Sensitive and Easy Detection of Hydrogen Peroxide

Hydrogen peroxide (H₂O₂) has been a fascinating target in various chemical, biological, clinical, and industrial fields. Several types of fluorescent protein-stabilized gold nanoclusters (protein-AuNCs) have been developed for sensitive and easy detection of H₂O₂. However, its low sensitivity makes is difficult to measure negligible concentrations of H₂O₂. Therefore, to overcome this limitation, we developed a horseradish peroxidase-encapsulated fluorescent bio-nanoparticle (HEFBNP), comprising bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) and horseradish peroxidase-stabilized gold nanoclusters (HRP-AuNCs). The fabricated HEFBNP can sensitively detect H₂O₂ owing to its two properties. The first is that HEFBNPs have a continuous two-step fluorescence quenching mechanism, which comes from the heterogenous fluorescence quenching mechanism of HRP-AuNCs and BSA-AuNCs. Second, the proximity of two protein-AuNCs in a single HEFBNP allows a reaction intermediate (•OH) to rapidly reach the adjacent protein-AuNCs. As a result, HEFBNP can improve the overall reaction event and decrease the loss of intermediate in the solution. Due to the continuous quenching mechanism and effective reaction event, a HEFBNP-based sensing system can measure very low concentrations of H₂O₂ up to 0.5 nM and show good selectivity. Furthermore, we design a glass-based microfluidic device to make it easier use HEFBNP, which allowed us to detect H₂O₂ with the naked eye. Overall, the proposed H₂O₂ sensing system is expected to be an easy and highly sensitive on-site detection tool in chemistry, biology, clinics, and industry fields.

Ratiometric fluorescent detection of silver nanoparticles in aqueous samples using peptide-based fluorogenic probes with aggregation-induced emission characteristics

The quantification of silver nanoparticles and Ag⁺ contamination in the aquatic ecosystem has attracted considerable interest. Benzoimidazolyl-cyanovinylene (1) was synthesized as an aggregation-induced emission fluorophore, and a fluorescent peptidyl probe (2 and 3) bearing this fluorophore was developed. The fluorescent peptidyl probes coordinated with Ag⁺ selectively among various metal ions, leading to a ratiometric response to Ag⁺ in pure aqueous solutions. Furthermore, an "in situ" protocol was developed to quantify AgNPs using 2 with H₂O₂ as an oxidizing reagent. The fluorescent detection method for Ag⁺ and AgNPs showed promising detection properties such as high selectivity, high sensitivity, fast response, visible light excitation, well-operations in pure aqueous solution, and large fluorescent signal change. The detection limits of Ag⁺ (0.64 ppb) and AgNPs (1.1 ppb) were significantly low. According to the binding mode study, Ag⁺ induced the formation of a 2:1 complex between 2 and Ag⁺ and the chirality of the peptide part of the probe was not critical for this process. The formation of aggregates of the probe triggered by Ag⁺ from AgNPs induced a significant change in fluorescence. Furthermore, the amounts of spiked AgNPs in groundwater and tap water were quantified using the fluorescent detection method with 2.

A sensitive fluorometric sensor for Ag+ based on the hybridization chain reaction coupled with a glucose oxidase dual-signal amplification strategy

In this work, an efficient and sensitive fluorometric sensor was developed to detect silver ions (Ag⁺). It is based on the cytosine–Ag⁺–cytosine (C–Ag⁺–C) structure via a dual-signal amplification strategy using glucose oxidase (GOx) and the hybridization chain reaction (HCR). A silver-coated glass slide (SCGS) acts as an ideal material for separation. Cytosine rich (C-rich) capture DNA (C-DNA) assembled themselves on the SCGS via Ag–S bonds and hybridized with signal DNA (S-DNA) to trigger the HCR. With specific base-pairing, the S-DNA and HCR products bind on the SCGS. Then, the GOx–biotin–streptavidin (SA) complexes bind to the HCR products through SA–biotin interactions. Owing to the formation of a particular C–Ag⁺–C structure between two neighboring C-rich C-DNA on the SCGS, the C-DNA/S-DNA/HP1-GOx/HP2-GOx complex gradually moved away from the SCGS as the concentration of Ag⁺ increased and the combined GOx fell into the buffer. H₂O₂ could be generated during the oxidation of glucose, catalyzed by GOx in the buffer. Afterward, H₂O₂ could oxidize the substrate (3-(p-hydroxyphenyl)-propanoic acid) when Horseradish peroxidase was present, giving rise to blue fluorescence. The proposed strategy reached a limit of detection (LOD) of 1.8 pmol L⁻¹ with a linear detection range of 5 to 1000 pmol L⁻¹ for Ag⁺. Moreover, this assay has been commendably used for the detection of Ag⁺ in actual samples with fairly good results.

An assay for Ag⁺ based on a C–Ag⁺–C structure by utilizing a HCR/GOx dual-signal amplification strategy and SCGS as an ideal separation material.

A simple and fast protocol for the synthesis of 2-amino-4-(4-formylphenyl)-4H-chromene-3-carbonitrile to develop an optical immunoassay for the quantification of botulinum neurotoxin type F

In this study, a novel optical immunoassay platform using (S)-2-amino-4-(4-formylphenyl)-4H-chromene-3-carbonitrile, which was synthesized by an ultra-sonication method, as an optical probe.

Unusual Fluorescence Behavior of Pyrene-Amine Containing Dendrimers

A new class of pyrene-based dendrimers, characterized by the presence of a 1,4,7,10-Tetraazacyclododecane (cyclen) unit as the core, was studied by SSF (steady-state fluorescence) and SPC (single-photon counting fluorescence). The photophysical behavior of these dendrimers was studied in THF, DMF and DMSO solution. The typical signals for pyrene-labeled molecules were recorded in each solvent, showing the representative fluorescence spectra: the corresponding emissions of monomer and excimer of the pyrene chromophore are observed. Unexpectedly, the typical quenching of tertiary amine on the pyrene emission was not observed in these dendrimers. Quenching studies were performed by adding up to 3 equivalents of trifluoroacetic acid (TFA). To our knowledge, this is the first report of pyrene's unquenching behavior by a tertiary amine.

A selective fluorescence probe based on naphthalene for the detection of barium(II)

A designed naphthalene derivative (potassium 2,2'-(naphthalen-1-ylazanediyl)diacetate, ND) was synthesized successfully which characterized by spectroscopic techniques (NMR, IR and HRMS-ESI-TOF). The sensitivity and selectivity were high toward Ba²⁺ in aqueous solution (100.0 mM HEPES buffer, 100.0 mM KNO₃, pH 7.4) over a wide variation of metal ions such as Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺, Al³⁺, Pb²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu⁺, Cu²⁺, Ag⁺, Zn²⁺, Cd²⁺ and Ce³⁺. The limit of detection (LOD) was found to be 9.56×10^-8 M. Density functional theory (DFT) calculations at the B3LYP level employing the 6-31G(d,p) and LANL2DZ basis set were performed for optimization of ND and ND-Ba²⁺ complex. The calculated results were consistent with a favorable complexation corresponding to the proposed coordination.

Design and Investigation of Optical Properties of N-(Rhodamine-B)-Lactam-Ethylenediamine (RhB-EDA) Fluorescent Probe

This study presents chemical modification of a Rhodamine B (RhB) sensor probe by ethylenediamine (EDA), and investigation of its spectral as well as sensor properties to the various metals. The synthesised N-(Rhodamine-B)-lactam-ethylenediamine (RhB-EDA) fluorescent probe shows interesting optical sensor properties, and high sensitivity and selectivity to Ag⁺ ions among all the tested metal ions (K⁺, Mg2+, Cu2+, Ni2+, Fe2+, Pb2+, Na⁺, Mn2+, Li⁺, Al3+, Co2+, Hg2+, Sr2+, Ca2+, Ag⁺, Cd2+ and Zn2+), while the well-known Rhodamine B (RhB) fluorescent probe shows much less sensitivity to Ag⁺ ions, but high sensitivity to Fe2+ ions. The novel fluorescent sensor probe RhB-EDA has the capabilities to sense Ag⁺ ions up to µM ranges by using the fluorescence quenching approach. The probe displayed a dynamic response to Ag⁺ in the range of 0.43 × 10-3-10-6 M with a detection limit of 0.1 μM. The sensing system of an RhB-EDA novel fluorescent probe was optimised according to the spectral properties, effect of pH and buffer, photostability, incubation time, sensitivity, and selectivity. Since all the spectral and sensing properties were tested in green aqueous media, although many other similar sensor systems rely on organic solvent solutions, the RhB-EDA sensing probe may be a good candidate for measuring Ag⁺ ions in real-life applications.

Novel double layer film composed of reduced graphene oxide and Rose Bengal dye: design, fabrication and evaluation as an efficient chemosensor for silver(i) detection

A novel silver-chemosensor fabricated with reduced graphene oxide and Rose Bengal (RB) based on the interaction of Ag⁺ and RB.

A Tetraphenylethene-Naphthyridine-Based AIEgen TPEN with Dual Mechanochromic and Chemosensing Properties

Synthesis of new tetraphenylethene (TPE) conjugates via an innocuous route led to the revelation of a unique TPE-based aggregation-induced emissive fluorogen 3 (TPEN), which showed an interesting mechanochromic property when the emission was changed from blue to green upon grinding and green to blue upon fuming. The mechanochromic property of TPEN has been explored to prepare ink-free rewritable paper for security documentation. A detailed photophysical investigation of the TPE-naphthyridine scaffold led to the discovery of its high sensitivity to silver ions (Ag⁺) over other metal ions with a detection limit of 0.25 μM in an aqueous system. The stoichiometry of the complex of TPEN and silver ion was established to be 2:1 (TPEN:Ag⁺) on the basis of photophysical studies, mass analysis, and high-resolution mass spectrometry analysis.

Deposition of silver nanoparticles onto two dimensional BiOCl nanodiscs for enhanced visible light photocatalytic and biocidal activities

Silver modified 2D BiOCl showed excellent photocatalytic performance in degrading sulfanilamide and presented good antibacterial efficiency under visible light irradiation.