A machine learning-assisted fluorescent sensor array utilizing silver nanoclusters for coffee discrimination.

Coffee is a globally consumed commodity of substantial commercial significance. In this study, we constructed a fluorescent sensor array based on two types of polymer templated silver nanoclusters (AgNCs) for the detection of organic acids and coffees. The nanoclusters exhibited different interactions with organic acids and generated unique fluorescence response patterns. By employing principal component analysis (PCA) and random forest (RF) algorithms, the sensor array exhibited good qualitative and quantitative capabilities for organic acids. Then the sensor array was used to distinguish coffees with different processing methods or roast degrees and the recognition accuracy achieved 100%. It could also successfully identify 40 coffee samples from 12 geographical origins. Moreover, it demonstrated another satisfactory performance for the classification of pure coffee samples with their binary and ternary mixtures or other beverages. In summary, we present a novel method for detecting and identifying multiple coffees, which has considerable potential in applications such as quality control and identification of fake blended coffees.

Genetically encoded fluorescence lifetime biosensors: overview, advances, and opportunities.

Genetically encoded biosensors based on fluorescent proteins (FPs) are powerful tools for tracking analytes and cellular events with high spatial and temporal resolution in living cells and organisms. Compared with intensiometric readout and ratiometric readout, fluorescence lifetime readout provides absolute measurements, independent of the biosensor expression level and instruments. Thus, genetically encoded fluorescence lifetime biosensors play a vital role in facilitating accurate quantitative assessments within intricate biological systems. In this review, we first provide a concise description of the categorization and working mechanism of genetically encoded fluorescence lifetime biosensors. Subsequently, we elaborate on the combination of the fluorescence lifetime imaging technique and lifetime analysis methods with fluorescence lifetime biosensors, followed by their application in monitoring the dynamics of environment parameters, analytes and cellular events. Finally, we discuss worthwhile considerations for the design, optimization and development of fluorescence lifetime-based biosensors from three representative cases.

Photoluminescent gold nanoclusters as two-photon excited ratiometric pH sensor and photoactivated peroxidase.

A two-photon excited ratiometric fluorescent pH sensor is reported by combining L-cysteine-protected AuNCs (Cys@AuNCs) with fluorescein isothiocyanate (FITC). Cys@AuNCs were synthesized through a one-step self-reduction route and showed pH-responsive photoluminescence at 650 nm. Benefiting from the opposite pH response of Cys@AuNCs and FITC, the fluorescence ratio (F515 nm/F650 nm) of FITC&Cys@AuNCs provided a large dynamic range of 200-fold for pH measurement in the response interval of pH 5.0-8.0. Based on the excellent two-photon absorption coefficient of Cys@AuNCs, the sensor was expected to achieve sensitive quantitation of pH in living cells under two-photon excitation. In addition, colorimetric biosensing based on enzyme-like metal nanoclusters has attracted wide attention due to their low-cost, simplicity, and practicality. It is crucial to develop high catalytic activity nanozyme from the viewpoint of practical application. The synthesized Cys@AuNCs exhibited excellent photoactivated peroxidase-like activity with high substrate affinity and catalytic reaction rate, promising for rapid colorimetric biosensing of field analysis and the control of catalytic reactions by photostimulation.

Tree-based machine learning models assisted fluorescent sensor array for detection of metal ions based on silver nanocluster probe.

The growing concern over heavy metal pollution and its impact on the environment and human health has led to a proliferation of research on the detection and differentiation of heavy metal ions. A novel fluorescent sensor array utilizing only one single Ag-nanoclusters (Ag NCs) was developed for the efficient detection of six metal ions. The Ag NCs probe was prepared by using poly(methyl vinyl ether-alt-maleic acid) (PMVEM) as the ligand and has different fluorescence properties in water and dimethyl sulfoxide (DMSO). The interaction between metal ions and Ag NCs resulted in a characteristic fluorescence variation pattern which was subsequently analyzed using various tree-based machine learning models. We have compared different combinations of classification models and pre-processing methods of which the K-Nearest Neighbors Classifier with the first five linear discriminants has the highest accuracy. Through the integration of concentration models within a tree-based pipeline optimization framework, six unique concentration regression models were selected for each metal ion. In addition, the developed sensor array could identify metal ions in binary mixtures. And it still kept high accuracy for the classification of six target metal ions in river water. In conclusion, the proposed framework was found to be effective in the detection of heavy metal ions in environmental samples, thus providing a promising approach for addressing heavy metal pollution.

A novel fluorescent sensor array to identify Baijiu based on the single gold nanocluster probe.

Baijiu occupies a vital position in Chinese food and China's market. Strict evaluation of Baijiu is highly demanded. In this study, we constructed a novel fluorescent sensor array based on the single glutathione-protected gold nanoclusters (AuNCs) probe for the detection of organic acids and Baijiu. The fluorescence of AuNCs was simply modulated by three metal ions (Cu2+, Mn2+, and Ag+), and formed new complexes as sensing elements. These four sensing elements responded variously to nine organic acids, and further chemometric analysis results allowed for the classification and quantification of acids. Moreover, the sensor array successfully identified 21 Baijiu samples of different brands among 11 aroma types. It could also distinguish Baijiu of different qualities as well as pure Baijiu from its adulterations and showed high selectivity among multiple interfering drinks. The results demonstrated that the AuNCs-based sensor array has considerable potential for quality monitoring of Baijiu.

Copper nanoclusters-based fluorescent sensor array to identify metal ions and dissolved organic matter.

In recent years, the prevention and control of water pollution has received extensive attention. There is a need to develop simple and effective strategies for the rapid detection of metal ions and dissolved organic matter (DOM) in order to improve water quality. To this end, the first copper nanoclusters (CuNCs)-based fluorescent sensor array was done to identify 12 metal ions (Pb2+, Fe3+, Cu2+, Cd2+, Cr3+, Co2+, Ni2+, Zn2+, Ag+, Fe2+, Hg2+, and Al3+) and DOM (humic substances, lipids, fatty acids, amino acids, and lignans). The results revealed that CuNCs that were synthesized with polyethyleneimine (PEI), histidine (His), and glutathione (GSH) exhibited different binding abilities to metal ions and DOM. These unique fluorescence responses were analyzed using principal component analysis (PCA) and linear discriminant analysis (LDA) to identify metal ions and DOM in the buffer. The aforementioned 12 metal ions were classified at a limit concentration of 1.5 µM. Moreover, quantification of metal ions was achieved even at a low concentration of 0.83 µM (Zn2+). This array also worked well in the recognition of metal ions in tap water as well as distinguishing riverine and seawater samples of different regions, which was of great significance in environmental monitoring.

Recent Development of Fluorescent Light-Up RNA Aptamers.

Technologies for RNA imaging in live cells play an important role in understanding the function and regulatory process of RNAs. One approach for genetically encoded fluorescent RNA imaging involves fluorescent light-up aptamers (FLAPs), which are short RNA sequences that can bind cognate fluorogens and activate their fluorescence greatly. Over the past few years, FLAPs have emerged as genetically encoded RNA-based fluorescent biosensors for the cellular imaging and detection of various targets of interest. In this review, we first give a brief overview of the development of the current FLAPs based on various fluorogens. Then we further discuss on the photocycles of the reversibly photoswitching properties in FLAPs and their photostability. Finally, we focus on the applications of FLAPs as genetically encoded RNA-based fluorescent biosensors in biosensing and bioimaging, including RNA, non-nucleic acid molecules, metal ions imaging and quantitative imaging. Their design strategies and recent cellular applications are emphasized and summarized in detail.

Colorimetric detection of water content in organic solvents via a smartphone with fluorescent Ag nanoclusters.

We detected the water content in ethanol and dimethyl sulfoxide (DMSO) solvents via a smartphone with the help of fluorescent Ag nanoclusters (Ag NCs). The Ag NCs intrinsically have two emission peaks, among which the long-wavelength emission intensified with decreasing water content due to the aggregation induced emission enhancement (AIEE) effect, but in contrast the short-wavelength emission was relatively insensitive to water content. This fact makes the Ag NCs an ideal colorimetric indicator of water content in organic solvents. A smartphone was applied to take pictures of Ag NC samples and read the R, G, and B values from the images. When the water content increased from 20% to 55% in ethanol, the G/B values displayed a good linear relationship with the water content, and a limit of detection (LOD) of 4.48% was achieved. Moreover, good consistency was observed when the colorimetric fluorescent Ag NCs were applied to detect water content in real samples such as white wine and medical alcohol. These studies demonstrated a convenient and practical method for the detection of water content via a smartphone.

The synthesis of metal nanoclusters and their applications in bio-sensing and imaging.

Noble metal nanomaterials have been studied by many researchers for their ultra-small size, excellent photophysical properties and good biocompatibility. Metal nanoclusters are a kind of nanoscale ultrafine particle, which have completely different properties from macroscopic metals. In the visible region, they do not usually show the characteristic surface plasmon resonance absorption but instead show fluorescence in the visible to near infrared region. In particular, the noble metallic (Au, Ag, Cu, etc) nanoclusters (NMNCs) have broad application prospects in the field of biomedicine as probes for fluorescence sensing. Their strong photoluminescence, living cell compatibility, and easy availability make up for the shortcomings of traditional fluorescent probes such as organic fluorescent dyes, fluorescent proteins, and fluorescent quantum dots. In this review, we summarize the synthetic method and application of metal nanoclusters as fluorescent probes in bio-sensing and imaging, especially in the early diagnosis of cancer cells.

Turn-on fluorescence detection of cysteine with glutathione protected silver nanoclusters.

In this work, we report a sensitive and selective turn-on fluorescence detection of cysteine with glutathione protected silver nanoclusters (GSH-Ag NCs). The glutathione stabilized silver nanoclusters were synthesized by the boiling water method. When excited at 380 nm, the GSH-Ag NCs exhibited a weak emission at about 680 nm, which could be enhanced by cysteine. The proposed method allows evaluation of cysteine in the range of 2-3000 µM with a detection limit of 0.51 µM. The recoveries were found to be 95.07%-101.38% when detecting cysteine contents in fetal bovine serum samples. In addition, we also discussed the possible mechanism for the fluorescence enhancement of GSH-Ag NCs by addition of cysteine. It might be the formation of cysteine and glutathione co-capped Ag NCs. This work reported a fluorimetric method for the assay of cysteine and provided a strategy for the synthesis of dual ligand-protected Ag nanoclusters.