Rapid Screening of Oxygen States in Carbon Quantum Dots by Chemiluminescence Probe

The oxygen states (O-states) of carbon quantum dots (CDs) play an important role, with regard to their optical properties and analytical applications. However, the rapid screening of O-states in CDs is still a great challenge, because of the complicated surface composition. In this study, it is found that the chemiluminescence (CL) intensity of prepared CDs in the presence of peroxynitrite (ONOO^–) is proportional to the content of C–O group-related O-states. The related mechanism discloses that the O-state-dependent CL is due to the fact that abundant C–O functional groups in CDs with high O-states could facilitate the electron transfer of the produced smaller energy gaps for strong CL emission. Hence, ONOO^–-induced CL can be utilized as a facile probe for the rapid screening of O-states in CDs with some advantages, such as rapid response, low cost, and easy operation. Its practicability is verified by detecting the CL of phosphorus-doped CDs with variable phosphorus-doping contents. The content of C–O group-related O-states in sulfur-/phosphorus-doped CDs measured by the proposed CL probe is consistent with X-ray photoelectron spectroscopy (XPS) characterization. This strategy can also be extended to distinguish O-states in different types of nanoparticles by tuning the CL probe molecules

Sensitive and Selective Detection of Copper Ions with Highly Stable Polyethyleneimine-Protected Silver Nanoclusters

Copper is a highly toxic environmental pollutant with bioaccumulative properties. Therefore, sensitive Cu²⁺ detection is very important to prevent over-ingestion, and visual detection using unaugmented vision is preferred for practical applications. In this study, hyperbranched polyethyleneimine-protected silver nanoclusters (hPEI-AgNCs) were successfully synthesized using a facile, one-pot reaction under mild conditions. The hPEI-AgNCs were very stable against extreme pH, ionic strength, temperature, and photoillumination and could act as sensitive and selective Cu²⁺ sensing nanoprobes in aqueous solutions with a 10 nM limit of detection. In addition, hPEI-AgNCs-doped agarose hydrogels were developed as an instrument-free and regenerable platform for visual Cu²⁺ and water quality monitoring

Color Difference Amplification between Gold Nanoparticles in Colorimetric Analysis with Actively Controlled Multiband Illumination

Spectral chemical sensing with digital color analysis by using consumer imaging devices could potentially revolutionize personalized healthcare. However, samples with small spectral variations often cannot be differentiated in color due to the nonlinearity of color appearance. In this study, we address this problem by exploiting the color image formation mechanism in digital photography. A close examination of the color image processing pipeline emphasizes that although the color can be represented digitally, it is still a reproducible subjective perception rather than a measurable physical property. That makes it possible to physically manage the color appearance of a nonradiative specimen through engineered illumination. By using scattering light imaging of gold nanoparticles (GNPs) as a model system, we demonstrated via simulation that enlarged color difference between spectrally close samples could be achieved with actively controlled illumination of multiple narrow-band light sources. Experimentally, darkfield imaging results indicate that color separation of single GNPs with various sizes can be significantly improved and the detection limit of GNP aggregation-based colorimetric assays can be much reduced when the conventional spectrally continuous white light was replaced with three independently intensity-controlled laser beams, even though the laser lines were uncorrelated with the LSPR maxima of the GNPs. With low-cost narrow-band light sources widely available today, this actively controlled illumination strategy could be utilized to replace the spectrometer in many spectral sensing applications

Probing the Alcoholysis Degree of Polyvinyl Alcohol by Synergistic Coordination-Regulated Fluorescence

Polyvinyl alcohol (PVA) with abundant hydroxyl groups (−OH) has been widely used for membranes, hydrogels, and films, and its function is largely affected by the alcoholysis degree. Therefore, the development of rapid and accurate methods for alcoholysis degree determination in PVAs is important. In this contribution, we have proposed a novel fluorescence-based platform for probing the alcoholysis degree of PVA by using the (E)-N-(4-methoxyphenyl)-1-(quinolin-2-yl)methanimine (QPM)-Zn2+ complex as the reporter. The mechanism study disclosed that the strong coordination between −OH and Zn2+ induced the capture of the QPM-Zn2+ complex and promoted its subsequent immobilization into the noncrystalline area. The immobilization of the QPM-Zn2+ complex restricted its molecular rotation and reduced the nonirradiative transition, thus yielding bright emissions. In addition, the practical applications of this proposed method were further validated by the accurate alcoholysis degree determination of blind PVA samples with the confirmation of the National Standard protocol. It is expected that the developed fluorescence approach in this work might become an admissive strategy for screening the alcoholysis degree of PVA

Fluorescent Gold Nanodots Based Sensor Array for Proteins Discrimination

A series of dual-ligand cofunctionalized fluorescent gold nanodots with similar fluorescence and diverse surface properties has been designed and synthesized to build a protein sensing array. Using this “chemical nose/tongue” strategy, fluorescence response patterns can be obtained on the array and identified via linear discriminant analysis (LDA). Eight proteins have been well distinguished at low concentration (<i>A</i>₂₈₀ = 0.005) based on this sensor array. The practicability of this sensor array was further validated by high accuracy (100%) examination of 48 unknown protein samples

Selective Colorimetric Detection of Hydrogen Sulfide Based on Primary Amine-Active Ester Cross-Linking of Gold Nanoparticles

Hydrogen sulfide (H₂S) is a highly toxic environmental pollutant and also an important gaseous transmitter. Therefore, selective detection of H₂S is very important, and visual detection of it with the naked eye is preferred in practical applications. In this study, thiolated azido derivates and active esters functionalized gold nanoparticles (AE-AuNPs)-based nanosensors have been successfully prepared for H₂S perception. The sensing principle consists of two steps: first, H₂S reduces the azide group to a primary amine; second, a cross-linking reaction between the primary amine and active ester induces the aggregation of AuNPs. The AE-AuNPs-based nanosensors show high selectivity toward H₂S over other anions and thiols due to the specific azide–H₂S chemistry. Under optimal conditions, 0.2 μM H₂S is detectable using a UV–vis spectrophotometer, and 4 μM H₂S can be easily detected by the naked eye. In addition, the practical application of the designed nanosensors was evaluated with lake water samples

Self-Assembled Chiral Gold Supramolecules with Efficient Laser Absorption for Enantiospecific Recognition of Carnitine

Stereospecific recognition of chiral molecules is ubiquitous in chemical and biological systems, thus leading to strong demand for the development of enantiomeric drugs, enantioselective sensors, and asymmetric catalysts. In this study, we demonstrate the ratio of d-Cys and l-Cys playing an important role in determining the optical properties and the structures of self-assembled Cys–Au­(I) supramolecules prepared through a simple reaction of tetrachloroaurate­(III) with chiral cysteine (Cys). The irregularly shaped −[d-Cys–Au­(I)]_<i>n</i>– or – [l-Cys–Au­(I)]_<i>n</i>– supramolecules with a size larger than 500 nm possessing strong absorption in the near-UV region and chiroptical characteristics were only obtained from the reaction of Au­(III) with d-Cys or l-Cys. On the other hand, spindle-shaped −[d/l-Cys–Au­(I)]_<i>n</i>– supramolecules were formed when using Au­(III) with mixtures of d/l-Cys. Our results have suggested that Au­(I)···Au­(I) aurophilic interactions, and stacked hydrogen bonding and zwitterionic interactions between d/l-Cys ligands are important in determining their structures. The NaBH₄-mediated reduction induces the formation of photoluminescent gold nanoclusters (Au NCs) embedded in the chiral −[d-Cys–Au­(I)]_<i>n</i>– or −[l-Cys–Au­(I)]_<i>n</i>– supramolecules with a quantum yield of ca. 10%. The as-formed Au NCs/–[d-Cys–Au­(I)]_<i>n</i>– and Au NCs/–[l-Cys–Au­(I)]_<i>n</i>– are an enantiospecific substrate that can trap l-carnitine and d-carnitine, respectively, and function as a nanomatrix for surface-assisted laser desorption/ionization mass spectrometry (LDI-MS). The high absorption efficiency of laser energy, analyte-binding capacity, and homogeneity of the Au NCs/–[Cys–Au­(I)]_<i>n</i>– allow for quantitation of enantiomeric carnitine down to the micromolar regime with high reproducibility. The superior efficiency of the Au NCs/–[d-Cys–Au­(I)]_<i>n</i>– substrate has been further validated by quantification of l-carnitine in dietary supplements with accuracy and precision. Our study has opened a new avenue for chiral quantitation of various analytes through LDI-MS using metal nanocomposites consisting of NCs and metal–ligand complexes