Etching and anti-etching strategy for sensitive colorimetric sensing of H2O2 and biothiols based on silver/carbon nanomaterial

A rapid near-infrared turn on fluorescence probe for the detection of sulfite in food and its application in biological imaging

A near-infrared fluorescent "turn on" probe DTMI featuring simple skeleton was constructed easily. It undergoes a structure transformation from an A-π-A to a D-π-A framework towards SO32-. Besides, DTMI is capable of distinctive sensing sulfite with a fast response and a significant Stokes shift as well as with high sensitivity, excellent selectivity, long-term stability of fluorescence signals, and good anti-interference ability. The detection limit (LOD) of DTMI for sulfite within the linear concentration range of 0.5-10 μM is 27.39 nM. More importantly, DTMI has been favorably utilized for detecting sulfite in food samples such as red wine and vermicelli. Based on its low biotoxicity, DTMI has been successfully applied in imaging experiments involving HeLa cells, onion inner epidermal cells, and zebrafish. Therefore, the results show that the presented probe possesses potential sensing activity towards sulfite in complex biological system and food samples.

Old drug, new use: The thalidomide-based fluorescent probe for cysteine detection and imaging in living cells

Thalidomide, as a high-profile cereblon (CRBN) ligand, has attracted much attention because of its ability to target protein degradation. In this study, we are committed to developing a new fluorescent probe THD-1 based on thalidomide, aiming at improving the performance of cysteine fluorescent probe in optical properties and biocompatibility. The experimental results showed that THD-1, as a cysteine fluorescent probe, owned the characteristics of obvious colorimetric change, fast response time, good selectivity and high sensitivity. The mechanism of THD-1 sensing cysteine was further verified to ensure its reliability and effectiveness. It was also worth mentioning that THD-1 was successfully applied to the biological imaging of cysteine in living A549 cells, which highlighted its value in practical application. Overall, thalidomide, as a clinically approved drug, not only enriches the fluorescent skeleton library, but also paves a new way for the further development of fluorescent probes.

Fluorescent/Colorimetric Dual-Mode Discriminating Gln and Val Enantiomers Based on Carbon Dots

Discrimination and quantification of amino acid (AA) enantiomers are particularly important for diagnosing and treating diseases. Recently, dual-mode probes have gained a lot of research interest because they can catch more detecting information compared with the single-mode probes. Thus, it is of great significance to develop a dual-mode sensor realizing AA enantiomer discrimination conveniently and efficiently. In this work, carbon dot L-TCDs were prepared by N-methyl-1,2-benzenediamine dihydrochloride (OTD) and l-tryptophan. With the assistance of H2O2, L-TCDs show an excellent discrimination performance for enantiomers of glutamine (Gln) and valine (Val) in both fluorescent and colorimetric modes. The fluorescence enantioselectivity of Gln (FD/FL) and Val (FL/FD) is 5.29 and 4.13, respectively, and the colorimetric enantioselectivity of Gln (ID/IL) and Val (IL/ID) is 13.26 and 3.42, individually. The chiral recognition mechanism of L-TCDs was systematically studied. L-TCDs can be etched by H2O2, and the participation of AA enantiomers results in different amounts of the released OTD, which provides fluorescent and colorimetric signals for identifying and quantifying the enantiomers of Gln and Val. This work provides a more convenient and flexible dual-mode sensing strategy for discriminating AA enantiomers, which is expected to be of great value in facile and high-throughput chiral recognition.

Colorimetric detection of biothiols and Hg2+ based on the peroxidase-like activity of GTP

Guanosine-5'-triphosphate (GTP) not only plays a key role in a majority of cellular processes but also be proposed as a peroxidase-like mimic. Compared with nanozymes, GTP shows good tolerance under harsh conditions, which can be used to construct an easy colorimetric analysis for the detection of biomolecules. Here, on the basis of the peroxidase-like activity of GTP which can catalyze the oxidation of 3,3',5,5'-tetramethyl benzidine dihydrochloride (TMB), colorimetric sensing was established for biothiols and Hg²⁺. Biothiols reduced the oxTMB back to colorless TMB, and Hg²⁺ restored the formation of oxTMB, leading to the recovery of color. This method not only provides a platform for the detection of metal ions and biothiols, but also shows that GTP has great potential for analytical detection.

Comparative Colorimetric Sensor Based on Bi-Phase γ-/α-Fe2O3 and γ-/α-Fe2O3/ZnO Nanoparticles for Lactate Detection

This work reports on Fe2O3 and ZnO materials for lactate quantification. In the synthesis, the bi-phase γ-/α-Fe2O3 and γ-/α-Fe2O3/ZnO nanoparticles (NPs) were obtained for their application in a lactate colorimetric sensor. The crystalline phases of the NPs were analyzed by XRD and XPS techniques. S/TEM images showed spheres with an 18 nm average and a needle length from 125 to 330 nm and 18 nm in diameter. The γ-/α-Fe2O3 and γ-/α-Fe2O3/ZnO were used to evaluate the catalytic activity of peroxidase with the substrate 3,3,5,5-tetramethylbenzidine (TMB), obtaining a linear range of 50 to 1000 μM for both NPs, and a 4.3 μM and 9.4 μM limit of detection (LOD), respectively. Moreover, γ-/α-Fe2O3 and γ-/α-Fe2O3/ZnO/lactate oxidase with TMB assays in the presence of lactate showed a linear range of 50 to 1000 µM, and both NPs proved to be highly selective in the presence of interferents. Finally, a sample of human serum was also tested, and the results were compared with a commercial lactometer. The use of ZnO with Fe2O3 achieved a greater response toward lactate oxidation reaction, and has implementation in a lactate colorimetric sensor using materials that are economically accessible and easy to synthesize.

SERS and Indicator Paper Sensing of Hydrogen Peroxide Using Au@Ag Nanorods

The detection of hydrogen peroxide and the control of its concentration are important tasks in the biological and chemical sciences. In this paper, we developed a simple and quantitative method for the non-enzymatic detection of H₂O₂ based on the selective etching of Au@Ag nanorods with embedded Raman active molecules. The transfer of electrons between silver atoms and hydrogen peroxide enhances the oxidation reaction, and the Ag shell around the Au nanorod gradually dissolves. This leads to a change in the color of the nanoparticle colloid, a shift in LSPR, and a decrease in the SERS response from molecules embedded between the Au core and Ag shell. In our study, we compared the sensitivity of these readouts for nanoparticles with different Ag shell morphology. We found that triangle core-shell nanoparticles exhibited the highest sensitivity, with a detection limit of 10^-4 M, and the SERS detection range of 1 × 10^-4 to 2 × 10^-2 M. In addition, a colorimetric strategy was applied to fabricate a simple indicator paper sensor for fast detection of hydrogen peroxide in liquids. In this case, the concentration of hydrogen peroxide was qualitatively determined by the change in the color of the nanoparticles deposited on the nitrocellulose membrane.

Naked-eye detection of cysteine/homocysteine through silver nano-resonators and specific identification of homocysteine through nanoresonator–thiosulphate conjugate

The citrate capped AgNPs synthesized through a modified previous report exhibit naked eye sensing towards cysteine/homocysteine along with SERS characteristics. Their thiosulphate conjugate detects selectively only homocysteine.

A carbon dots functionalized paper coupled with AgNPs composites platform: application as a sensor for hydrogen peroxide detection based on surface plasmon-enhanced energy transfer

A paper-based fluorescent sensor (PCD/AgNPs) consisted of CDs functionalized paper and AgNPs was developed for sensing H₂O₂ in milk samples and cancer cells.

pH-Dependent photoluminescence “switch-on” nanosensors composed of silver nanoparticles and nitrogen and sulphur co-doped carbon dots for discriminative detection of biothiols

A nanomaterial surface energy transfer (NSET) system composed of silver nanoparticles (AgNPs) and nitrogen and sulphur co-doped carbon dots (N,S-CDs) was established to discriminate biothiols, featuring the pH-promoted distinct PL “switch-on” response.