Real‐time Tracking and Sensing of Cu + and Cu 2+ with a Single SERS Probe in the Live Brain: Toward Understanding Why Copper Ions Were Increased upon Ischemia

Architecture of Easy-to-Synthesize and Superior Probe Based on Aminoquinoline Appended Naphthoquinone: Instant and On-Site Cu2+ Ion Quantification in Real Samples and Unusual Crystal Structure and Logic Gate Operations

Easy-to-synthesize aminoquinoline (AQ) appended naphthoquinone (NQ)-based colorimetric and ratiometric probe (AQNQ) was successfully synthesized in one step with high yield and low cost, and was utilized to supply an effective solution to critical shortcomings encountered in Cu2+ analysis. The structure of AQNQ and its interaction with Cu2+ forming an unusual AQNQ-Cu complex were enlightened with single-crystal X-ray diffraction analysis and different spectroscopic methods. AQNQ-Cu complex is the first Cu2+ containing dinuclear crystal where the octahedral coordination sphere is fulfilled through the coordination of a NQ oxygen atom. AQNQ exhibited long-term stability (more than 1 month), superior probe ability toward Cu2+ with quite fast response (30 s), high selectivity among many ions, and limit of detection of 12.13 ppb that is significantly below the highest amount of Cu2+ allowed in drinking water established by both WHO and EPA. Ratiometric determination of Cu2+ using AQNQ was performed with high recovery and low RSD values for drinking water, tap water, lake water, cherry, and watermelon samples. Colorimetric on-site determination including smartphone and paper strip applications, IMPLICATION, and INHIBIT logic gate applications were successfully carried out. The reversibility and reusability of the response to Cu2+ ions with the paper strip application were examined for the first time.

A Ratiometric SERS Probe for Imaging the Macrophage Phenotypes in Live Mice with Epilepsy and Brain Tumor

Macrophage performs multiple functions such as pathogen phagocytosis, antigen presentation, and tissue remodeling by polarizing toward a spectrum of phenotypes. Dynamic imaging of macrophage phenotypes is critical for evaluating disease progression and the therapeutic response of drug candidates. However, current technologies cannot identify macrophage phenotypes in vivo. Herein, a surface-enhanced Raman scattering nanoprobe, AH1, which enables the accurate determination of physiological pH with high sensitivity and tissue penetration depth through ratiometric Raman signals is developed. Due to the phenotype-dependent metabolic reprogramming, AH1 can effectively identify macrophage subpopulations by measuring the acidity levels in phagosomes. After intravenous administration, AH1 not only visualizes the spatial distribution of macrophage phenotypes in brain tumors and epileptic regions of mouse models, but also reveals the repolarization of macrophages in brain lesions after drug intervention. This work provides a new tool for dynamically monitoring the disease-associated immune microenvironment and evaluating the efficacy of immune-therapeutics in vivo.

An explainable machine-learning approach for revealing the complex synthesis path-property relationships of nanomaterials

Machine learning (ML) models have recently shown important advantages in predicting nanomaterial properties, which avoids many trial-and-error explorations. However, complex variables that control the formation of nanomaterials exhibiting the desired properties still need to be better understood owing to the low interpretability of ML models and the lack of detailed mechanism information on nanomaterial properties. In this study, we developed a methodology for accurately predicting multiple synthesis parameter-property relationships of nanomaterials to improve the interpretability of the nanomaterial property mechanism. As a proof-of-concept, we designed glutathione-gold nanoclusters (GSH-AuNCs) exhibiting an appropriate fluorescence quantum yield (QY). First, we conducted 189 experiments and synthesized different GSH-AuNCs by varying the thiol-to-metal molar ratio and reaction temperature and time in reasonable ranges. The fluorescence QY of GSH-AuNCs could be systematically and independently programmed using different experimental parameters. We used limited GSH-AuNC synthesis parameter data to train an extreme gradient boosting regressor model. Moreover, we improved the interpretability of the ML model by combining individual conditional expectation, double-variable partial dependence, and feature interaction network analyses. The interpretability analyses established the relationship between multiple synthesis parameters and fluorescence QYs of GSH-AuNCs. The results represent an essential step towards revealing the complex fluorescence mechanism of thiolated AuNCs. Finally, we constructed a synthesis phase diagram exceeding 6.0 × 104 prediction variables for accurately predicting the fluorescence QY of GSH-AuNCs. A multidimensional synthesis phase diagram was obtained for the fluorescence QY of GSH-AuNCs by searching the synthesis parameter space in the trained ML model. Our methodology is a general and powerful complementary strategy for application in material informatics.

Reversible Recognition-Based Boronic Acid Probes for Glucose Detection in Live Cells and Zebrafish

Glucose, a critical source of energy, directly determines the homeostasis of the human body. However, due to the lack of robust imaging probes, the mechanism underlying the changes of glucose homeostasis in the human body remains unclear. Herein, diboronic acid probes with good biocompatibility and high sensitivity were synthesized based on an ortho-aminomethylphenylboronic acid probe, phenyl(di)boronic acid (PDBA). Significantly, by introducing the water-solubilizing group -CN directly opposite the boronic acid group and -COOCH₃ or -COOH groups to the β site of the anthracene in PDBA, we obtained the water-soluble probe Mc-CDBA with sensitive response (F/F₀ = 47.8, detection limit (LOD) = 1.37 μM) and Ca-CDBA with the highest affinity for glucose (K_a = 4.5 × 10³ M^-1). On this basis, Mc-CDBA was used to identify glucose heterogeneity between normal and tumor cells. Finally, Mc-CDBA and Ca-CDBA were used for imaging glucose in zebrafish. Our research provides a new strategy for designing efficient boronic acid glucose probes and powerful new tools for the evaluation of glucose-related diseases.

Real-Time Monitoring of Neurotransmitters in the Brain of Living Animals

Neurotransmitters, as important chemical small molecules, perform the function of neural signal transmission from cell to cell. Excess concentrations of neurotransmitters are often closely associated with brain diseases, such as Alzheimer's disease, depression, schizophrenia, and Parkinson's disease. On the other hand, the release of neurotransmitters under the induced stimulation indicates the occurrence of reward-related behaviors, including food and drug addiction. Therefore, to understand the physiological and pathological functions of neurotransmitters, especially in complex environments of the living brain, it is urgent to develop effective tools to monitor their dynamics with high sensitivity and specificity. Over the past 30 years, significant advances in electrochemical sensors and optical probes have brought new possibilities for studying neurons and neural circuits by monitoring the changes in neurotransmitters. This Review focuses on the progress in the construction of sensors for in vivo analysis of neurotransmitters in the brain and summarizes current attempts to address key issues in the development of sensors with high selectivity, sensitivity, and stability. Combined with the latest advances in technologies and methods, several strategies for sensor construction are provided for recording chemical signal changes in the complex environment of the brain.

Red-emitting carbon dots aggregates-based fluorescent probe for monitoring Cu2

R-CDAs have been synthesized in a one-pot solvothermal procedure starting from 3,4-diaminobenzoic acid in an acidic medium. Transmission electron microscopy (TEM) revealed that R-CDAs nanoparticles exhibited a much larger diameter of 7.2-28.8 nm than traditional monodisperse carbon dots. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) revealed the presence of polar functional groups (hydroxyl, amino, carboxyl) on the surface of R-CDAs. Upon excitation with visible light (550 nm), R-CDAs emit stable, red fluorescence with a maximum at 610 nm. Under the optimum conditions, Cu²⁺ ions quench the fluorescence of this probe, and the signal is linear in a concentration range of copper ions between 5 and 600 nM with the detection limit of only 0.4 nM. Recoveries from 98.0 to 105.0% and relative standard deviations (RSD) from 2.8 to 4.5% have been obtained for detection of Cu²⁺ in real water samples. Furthermore, the R-CDAs fluorescent probe showed negligible cytotoxicity toward HeLa cells and good bioimaging ability, suggesting its potential applicability as a diagnostic tool in biomedicine.

A Liquid Interfacial SERS Platform on a Nanoparticle Array Stabilized by Rigid Probes for the Quantification of Norepinephrine in Rat Brain Microdialysates

For the reliable determination of trace chemicals in the brain, we created a SERS platform based on a functionalized AuNPs array formed at a liquid/liquid interface in a uniform fashion over a large substrate area through ternary regulations for real-time quantification of trace norepinephrine (NE). The rigid molecule, 4-(thiophen-3-ylethynyl)-benzaldehyde (RP1) was designed and co-assembled at AuNPs with 4-mercaptophenylboronic acid (MPBA) to chemically define NE via dual recognition. Meanwhile, the rigid structure assembly of RP1 and MPBA efficiently fixed the interparticle gap, guaranteeing reproducible SERS analysis. Furthermore, the Raman peak of C≡C group in the silent region was taken as a response element to further improve the accuracy. Combined with microdialysis, this SERS platform was developed for in-the-field testing of NE in rat brain microdialysates following anxiety.