Sensing of Hydrogen Sulfide Gas in the Raman-Silent Region Based on Gold Nano-Bipyramids (Au NBPs) Encapsulated by Zeolitic Imidazolate Framework-8

Raman silent region - based method for detection of pesticides with cyano group

Based on the fact that not all chemical substances possess good Raman signals, this article focuses on the Raman silent region signals of pesticides with cyano group. Under the optimized conditions of methanol-water (1:1, v/v) as the solvent, irradiation at 302 nm light source for 20 min, and the use of 0.5 mol/L KI as the aggregating agent, Surface-enhanced Raman spectroscopy (SERS) method for azoxystrobin detection was developed by the Raman silent region signal of 2230 cm-1, and verified by detecting the spiked grapes with different concentrations of azoxystrobin. Other four pesticides with cyano group also could be identified at the peak of 2180 cm-1, 2205 cm-1, 2125 cm-1, and 2130 cm-1 for acetamiprid, phoxim, thiacloprid and cymoxanil, respectively. When azoxystrobin or acetamiprid was mixed respectively with chlorpyrifos without cyano group, their SERS signals in the Raman silent region of chlorpyrifos were not interfered, while mixed with cymoxanil in different ratios (1:4, 1:1 and 4:1), respectively, each two pesticides with cyano group could be distinguished by the changes in the Raman silent region. In further, four pesticides with or without cyano group were mixed together in 1:1:1:1 (acetamiprid, cymoxanil, azoxystrobin chlorpyrifos), and each pesticide still could be identified even at 0.5 mg/L. The results showed that the SERS method combined with UV irradiation may provide a new way to monitor the pesticides with C≡N performance in the Raman silent region without interference from the food matrix.

Portable Hadamard-Transform Raman Spectrometer: A Powerful Analytical Tool for Point-of-Care Testing

A portable Hadamard-transform Raman spectrometer with excellent performance was fabricated consisting of a 785 nm laser, an optical filter, an optical system, a control system, and a signal processing system. As the core of the spectrometer, the optical system was composed of a slit, collimator, optical grating, reflector, digital micromirror devices (DMD), lens system, and InGaAs photodetector. Compared with a conventional dispersive Raman spectrometer, the proposed Raman spectrometer adopted the DMD and corresponding controlling device (DLPC350 control chip) to collect the Raman spectrum. Thus, in our design, the gratings are fixed, while the full Raman spectrum was collected by the deflection of the micromirror. This design can greatly improve the vibration resistance ability of the spectrometer since the gratings are not rotating during the spectrum collecting. More importantly, Hadamard-transform was used as signal processing technology, which has the ability of faster calculation, the merits of high energy input, single detector multichannel simultaneous detection (imaging) ability, and high signal-to-noise ratio (SNR). Hence, the Hadamard-transform portable Raman spectrometer has the potential to be applied in the field of point-of-care testing (POCT).

One-Step Synthesis of Chitosan Hydrogel as Electrochemical Chemosensor for Hydrogen Sulfide Detection in Pregnancy-Induced Hypertension Syndrome Serum Sample

Oxidative stress caused by pregnancy-induced hypertension syndrome significantly affects the health of pregnant women. Hydrogen sulfide is a typical gaseous signal molecule against oxidative stress, and it is of profound significance to develop a detection method. In this study, a stimuli-responsive hydrogel was constructed based on the coordination and bonding principle of metal ions and chitosan (CS) to realize the quantitative detection of hydrogen sulfide (H2S). The chain of CS contains a large number of amino groups and hydroxyl groups, which can form the coordination structure with Cu2+, triggering CS to form a stable hydrogel. The hydrogel can be formed within about 5 s, which has the characteristics of rapid preparation. In the presence of target H2S, the cross-linking agent Cu2+ in the hydrogel can compete out, resulting in the collapse of the hydrogel and the release of the electrochemical probe. By detecting the concentration of the released electrochemical probe, the quantitative detection of H2S can be achieved. The prepared hydrogel has a good linear relationship with the concentration of H2S from 1 μM to 60 μm. At the same time, the hydrogel has good specificity and stability, and it can be applied to the detection of H2S in serum samples.

Temperature-sensitive metal-enhanced fluorescence and plasmon resonance energy transfer

Experimental decoupling of the effects of plasmon resonance energy transfer (PRET) and metal-enhanced fluorescence (MEF) within the same nanometal-fluorophore pair is fascinating but challenging. In this study, we presented a possible solution for this by coating plasmonic Au nanoparticles (AuNPs) with temperature-sensitive poly(N-isopropylacrylamide) (pNIPAM) shells and R6G hybrids, termed the Au@p-R nanoplatform, which could reversibly adjust the separation between dyes and the AuNP surface, enabling an ON/OFF switch between MEF and PRET. In our optimization process, we discovered that 20 kDa of pNIPAM causes an MEF effect owing to an appropriate shrinking distance of 6.86 ± 0.85 nm. This dual-model nanoplatform exhibits great potential for tracking temperature-dependent transitions.

Ratiometric SERS quantification of SO2 vapor based on Au@Ag-Au with Raman reporter as internal standard

Practical gas sensing application requires sensors to quantify target analytes with high sensitivity and reproducibility. However, conventional surface enhanced Raman scattering (SERS) sensor lacks reproducibility and quantification arising from variations of "hot spot" distribution and measurement conditions. Here, a ratio-dependent SERS sensor was developed for quantitative label-free gas sensing. Au@Ag-Au nanoparticles (NPs) were filtered onto anodic aluminum oxide (AAO) forming Au@Ag-Au@AAO SERS substrate. 4-MBA was encapsulated in the gap of Au@Ag-Au and served as the internal standard (IS) to calibrate SERS signal fluctuation for improved quantification ability. Combined with headspace sampling method, SO2 residue in traditional Chinese medicine (TCM) can be extracted and captured on the immediate vicinity of Au@Ag-Au surface. The intensity ratio I613 cm-1/I1078 cm-1 showed excellent linearity within the range of 0.5 mg/kg-500 mg/kg, demonstrating superior quantification performance for SO2 detection. Signals for concentration as low as 0.05 mg/kg of SO2 could be effectively collected, much lower than the strictest limit 10 mg/kg in Chinese Pharmacopoeia. Combined with a handheld Raman spectrometer, handy and quantitative TCM quality evaluation in aspect of SO2 residue was realized. This ratiometric SERS sensor functioned well in rapid on-site SO2 quantification, exhibiting excellent sensitivity and simple operability.

Background-Free SERS Nanosensor for Endogenous Hydrogen Sulfide Detection Based on Prussian Blue-Coated Gold Nanobipyramids

Surface-enhanced Raman scattering (SERS) has great potential in biological analysis due to its specificity, sensitivity, and non-invasive nature. However, effectively extracting Raman information and avoiding spectral overlapping from biological background interference remain major challenges. In this study, we developed a background-free SERS nanosensor consisting of gold nanobipyramids (Au NBPs) core-Prussian blue (PB) shell (Au NBPs@PB), for endogenous H2S detection. The PB shell degraded quickly upon contact with endogenous H2S, generating a unique Raman signal response in the Raman silent region (1800-2800 cm-1). By taking advantage of the high SERS-activity of Au NBPs and H2S-triggered spectral changes of PB, these SERS nanosensors effectively minimize potential biological interferences. The nanosensor exhibits a detection range of 2.0 μM to 250 μM and a limit of detection (LOD) of 0.34 μM, with good reproducibility and minimal interference. We successfully applied this background-free SERS platform to monitor endogenous H2S concentrations in human serum samples with satisfied results.

Bimetallic AuNR@AgNCs for ultrasensitive surface-enhanced Raman scattering sensing of dithianon in apple juice

In this study, a bimetallic surfaced-enhanced Raman spectroscopy (SERS)-active substrate consisting of AuNR@AgNCs was proposed for the rapid detection of dithianon. Due to the significant synergistic enhancement of the core-shell nanocuboids, the obtained AuNR@AgNC substrate exhibited excellent SERS performance. The simulation findings supported the practical SERS results and demonstrated that interactions were mainly maintained by the nitrile functional group. The AuNR@AgNCs could be used to detect dithianon with an LOD value of 20 nM. Moreover, dithianon in river water and apple juice could be detected with recovery in the satisfactory ranges of 97.41%-98.35% and 97.77%-98.70%, respectively, by using this substrate under optimal conditions, indicating that the AuNR@AgNC substrate could serve as an excellent SERS detection platform for pesticide residues in fruit.

Enzyme-catalyzed electrochemical aptasensor for ultrasensitive detection of soluble PD-L1 in breast cancer based on decorated covalent organic frameworks and carbon nanotubes

BACKGROUND

Soluble programmed death-ligand 1 (sPD-L1) is critically involved in breast cancer recurrence and metastasis. However, the clinical application of highly sensitive sPD-L1 assays remains a challenge due to its low abundance in peripheral blood. To address this issue, for the first time, an enzyme-catalyzed electrochemical aptasensing platform was devised, incorporating covalent organic frameworks-gold nanoparticles-antibody-horseradish peroxidase (COFs-AuNPs-Ab-HRP) and polyethyleneimine-functionalized multiwalled carbon nanotubes (MWCNTs-PEI-AuNPs) for the highly specific and ultrasensitive detection of sPD-L1.

RESULTS

MWCNTs-PEI-AuNPs possessed an extensive specific surface area and exhibited excellent electrical conductivity, facilitating the immobilization of aptamer and amplifying the signal. COFs modified with AuNPs not only amplified the electrical signal but also proffered a loading platform for the Ab and HRP. The favorable biocompatibility of COFs contributed to the preservation of enzyme activity and stability. HRP acted in synergy with hydrogen peroxide (H2O2) to catalyze the oxidation of hydroquinone (HQ) to benzoquinone (BQ). Subsequently, BQ underwent electrochemical reduction to HQ, inducing an enzymatic redox cycle that amplified the electrochemical signal and enhanced the sensitivity and selectivity of the detection method. The developed aptasensor displayed a liner range for sPD-L1 identification from 1 pg mL-1 to 100 ng mL-1 and the detection limit reached 0.143 pg mL-1 (S/N = 3).

SIGNIFICANCE

Paving the way for clinical application, this strategy detected differences in sPD-L1 in cell supernatants and peripheral blood of breast cancer patients with higher sensitivity compared to commercial sPD-L1 ELISA kit. This work demonstrates significant potential in offering reference information for early diagnosis and disease surveillance of breast cancer.

Magnetic MOF Substrates for the Rapid and Sensitive Surface-Enhanced Raman Scattering Detection of Uranyl

With the widespread use of uranium in the nuclear industry, achieving rapid and sensitive detection of uranium contaminants is critical for reducing environmental pollution. Surface-enhanced Raman scattering (SERS), with its high sensitivity and unique fingerprint properties, has been used for the analysis of uranyl. However, the weak affinity of Au for uranyl remains a challenge in the development of spherical Au-based SERS substrates. The metal-organic framework (MOF) material ZIF-8 exhibits excellent adsorption capacity for uranyl and could overcome this limitation. In this study, ZIF-8 porous structures were modified on a magnetic SERS substrate, Fe3O4@SiO2@Au (FA), for the rapid and sensitive detection and analysis of the uranyl species. Uranyl was adsorbed by ZIF-8, allowing ready access to the hot spots in the interstices of Au nanoparticles (AuNPs). Symmetrically stretched vibrating bonds of O═U═O were detected at 829 cm-1 as the characteristic peak of uranyl by surface plasmon resonance between the AuNPs. The ZIF-8 coating had minimal influence on target detection as the detection limit for 4-MPY was only half an order of magnitude lower than before modification. The enhancement factor for uranyl reached 106. The substrate showed excellent sensing performance in a neutral or alkaline environment. It was used to detect uranyl in tap water and river water; rapid separation of the species from the water samples was achieved using an external magnet to extract radioactive waste. The proposed substrate offers a route for monitoring and detecting uranyl contamination and an approach for achieving rapid on-site detection, providing a promising application for environmental contaminant detection.

A dual mode 'turn-on' fluorescence-Raman (SERS) response probe based on a 1H-pyrrol-3(2H)-one scaffold for monitoring H2S levels in biological samples

Discovery of the biological signaling roles of H2S has spurred great interest in developing reliable methods for its accurate detection and quantification. As considerable variation in its levels is seen during pathological conditions such as sepsis, real-time quantification methods have relevance in diagnosis as well. Of various approaches, reaction-based probes which respond through 'off-on' fluorescence emission remain the most studied. Since the intensity of emission is related to the analyte concentration in these measurements, the presence of built-in features which provide an opportunity for internal referencing will be advantageous. In view of this, a dual mode response system that senses H2S through characteristic fluorescence and Raman (SERS) signals based on a 1H-pyrrol-3(2H)-one scaffold was developed and is the main highlight of this report. This probe offers several advantages such as fast response (<1 min), and high selectivity and sensitivity with a detection limit of ∼7 nM. Imaging of H2S in HepG2 cells, making use of the SERS signal from the thiolysis product is also demonstrated.

A novel electrochemical sensor based on gold nanobipyramids and poly-L-cysteine for the sensitive determination of trilobatin

Trilobatin is a flavonoid that has wide application prospects due to its various pharmacological effects, such as anti-inflammation and anti-oxidation. In this work, a novel electrochemical sensor based on gold nanobipyramids (AuNBs) and L-cysteine (L-cys) was constructed for the sensitive and selective determination of trilobatin. The AuNBs, which were prepared by a seed-mediated growth method, had large specific surface areas and excellent electrical conductivity. A layer of L-cys film, which provided more active sites through the amino and hydroxyl groups, was modified on the surface of the AuNBs by electropolymerization. Significantly, the Au-S bond between the L-cys film and AuNBs could improve the stability of the sensor and it exhibited satisfactory electrocatalytic oxidation activity for trilobatin. Under optimized conditions, the sensor based on poly-L-cys/AuNBs/GCE was used to determine trilobatin by differential pulse voltammetry (DPV). Two wide linear ranges between the current peak and the concentration of trilobatin were obtained in the range from 5 to 100 μM and 100 to 1000 μM, and the low detection limit (LOD) was up to 2.55 μM (S/N = 3). The sensor demonstrated desirable reproducibility, stability, and selectivity and was applied to detect real trilobatin samples extracted from Lithocarpus polystachyus Rehd.'s leaves, showing recoveries of 98.36%-104.96%, with satisfactory results.

Colorimetric and visual determination of iodide ions via morphology transition of gold nanobipyramids

The gold nanobipyramids (Au NBPs) are widely used in the analytical detection of biochemistry due to their unique localized surface plasmon resonance (LSPR) properties. In our developed approach, I^- in kelp was detected by etching Au NBPs in the presence of IO₃^-. Under acidic conditions, IO₃^- reacted rapidly with I^- to form I₂, subsequently I₂ reacted with I^- to form the intermediate I₃^-. In the presence of CTAB, Au NBPs were etched by I₂ derived from I₃^-, resulting in a decrease in the aspect ratio of Au NBPs, to form a significant blue shift of LSPR longitudinal peak and color variation of colloid which changed from blue-green to magenta and could be employed to quantitatively detect the concentration of I^- with the naked eye. A linear relationship can be found between the LSPR peak changes with the I^- concentration in a wide range from 4.0 μM to 15.0 μM, and the sensitive limit of detection (LOD) was 0.2 μM for UV-vis spectroscopy and the obvious color changes with a visual LOD was 4.0 μM for the naked eye. Benefiting from the high specificity, the proposed colorimetric detection of I^- in kelp samples was achieved, indicating the available potential of the colorimetric detection for the determination of I^- in real samples. What's more, this detection procedure was time-saving and could avoid tedious procedures.

Engineered nanomaterials-based sensing systems for assessing the freshness of meat and aquatic products: A state-of-the-art review

Meat and aquatic products are susceptible to spoilage during distribution, transportation, and storage, increasing the urgency of freshness evaluation. Engineered nanomaterials (ENMs) typically with the diameter in the range of 1-100 nm exhibit fascinating physicochemical properties. ENMs-based sensing systems have received extensive attention for food freshness assessment due to the advantages of being fast, simple, and sensitive. This review focuses on summarizing the recent application of ENMs-based sensing systems for food freshness detection. First, chemical indicators related to the freshness of meat and aquatic products are described. Then, how to apply the ENMs including noble metal nanomaterials, metal oxide nanomaterials, carbon nanomaterials, and metal-organic frameworks for the construction of different sensing systems were described. Besides, the recent advance in ENMs-based colorimetric, fluorescent, electrochemical, and surface-enhanced Raman spectroscopy sensing systems for assessing the freshness of meat and aquatic products were outlined. Finally, the challenges and future research perspectives for the application of ENMs-based sensing systems were discussed. The ENMs-based sensing systems have been demonstrated as effective tools for freshness evaluation. The sensing performance of ENMs employed in different sensing systems depends on their composition, size, shape, and stability of nanoparticles. For the real application of ENMs in food industries, the risks and regulatory issues associated with nanomaterials need to be further considered. With the continuous development of nanomaterials and sensing devices, the ENMs-based sensors are expected to be applied in-field for rapid detection of the freshness of meat and aquatic products in the future.

Green Synthesis of Three-Dimensional Au Nanorods@TiO2 Nanocomposites as Self-Cleaning SERS Substrate for Sensitive, Recyclable, and In Situ Sensing Environmental Pollutants

In this work, a simple, low-cost, green, and mild method for the preparation of three-dimensional nanocomposite materials of gold nanorods (Au NRs)@TiO₂ is reported. The surface of Au NRs was coated with TiO₂ in situ reduction at room temperature without a complicated operation. The synthetic Au NRs@TiO₂ nanocomposites were used as surface-enhanced Raman spectroscopy (SERS) active substrates for the reusable and sensitive detection of environmental pollutants. The results showed that the pollutants on Au NRs@TiO₂ nanocomposites have higher SERS activity and reproducibility than those on the Au NR substrate without the presence of TiO₂. Moreover, the SERS substrate can be readily recycled by UV-assisted self-cleaning to remove residual analyte molecules. Malachite green (MG) and crystal violet (CV) were used as examples to demonstrate the feasibility of the proposed sensor for the sensitive detection of environmental pollutants. The results showed that the limit of detections (LODs) were 0.75 μg/L and 0.50 μg/L for MG and CV, respectively, with the recoveries ranging from 86.67% to 91.20% and 83.70% to 89.00%. Meanwhile, the SERS substrate can be easily regenerated by UV light irradiation. Our investigation revealed that within three cycles, the Au NRs@TiO₂ substrates still maintained the high SERS enhancement effect that they showed when first used for SERS detection. These results indicated that the method can be used to detect MG and CV in really complex samples. Due to the high sensitivity, reusability, and portability and the rapid detection property of the proposed sensor, it can have potential applications in the on-site detection of environmental pollutants in a complex sample matrix.

A Programmable Plasmonic Gas Microsystem for Detecting Arbitrarily Combinated Volatile Organic Compounds (VOCs) with Ultrahigh Resolution

For gas sensors, the ultrasensitive and highly selective detection of multiple components is of great significance in a wide range of applications extending from environment to healthcare, which is still a long-term challenge due to the single sensing mechanism of most sensors. Here, we combine the advantages of microfluidic chips and surface-enhanced Raman spectroscopy (SERS) spectra to fabricate a smart single-chip for simultaneously detecting an arbitrary combination of VOCs that incorporates different detection units, working on either a physisorption or chemisorption mechanism. Full integration of microfluidic and multiplex nanostructure components on one chip permits programmable design for sensing multifarious volatile compounds, and enables on-chip signal amplifications with increased reproducibility. As a proof-of-principle experiment, we demonstrate the simultaneous identification of 9 different gases that belong to aromatic compounds, aldehydes, ketones, or sulfides in one mixture, with high sensitivity (ppb level), high selectivity, and high robustness (error ∼8%). We further evaluated the application of our universal gas sensor in two scenarios including indoor air pollution monitoring and exhaled breath-based disease diagnosis. We expect that our design will improve the various practical applications of gas sensors.

SERS Monitored Kinetic Process of Gaseous Thiophenol Compound in Plasmonic MOF Nanoparticles

Benefiting from the electromagnetic enhancement of noble metal nanoparticles (NPs) and the capture ability of organic frameworks, plasmonic metal-organic framework (MOF) structures have greatly promoted the development of gas detection by surface-enhanced Raman spectroscopy (SERS). In those detections, the kinetic process of gaseous molecules in plasmonic-MOF structures has a great influence on SERS spectra, which is still lacking intensive investigation in previous reports. In this work, the kinetic processes of gaseous thiophenol compounds (TPC) in the plasmonic Zeolitic Imidazolate Framework (Ag@ZIF) core-shell NPs are studied by SERS spectra. The experimental data demonstrate that the SERS intensities of gaseous TPC could be enhanced once more in an H₂ mixed gas environment with different functional groups of TPC. Further results reveal that the two-step enhancement of SERS intensities is not only related to the thicknesses of the MOF shell but also affected by the ambient mixed gas. To understand this novel phenomenon, the binding energy between the gaseous molecule and ZIF is calculated based on first-principles computation. In combination with the plasmonic properties of the Ag core, a molecular collision model is introduced here to show the distribution of gaseous TPC molecules in ZIF, which could be responsible for this interesting two-step enhancement of SERS intensities. Furthermore, the H₂ assisted kinetic process of gaseous p-aminothiophenol (PATP) is also analyzed by the classical pseudo-first-order kinetic model, which is consistent with our experimental SERS data. Our work not only reveals the novel phenomenon of plasmonic-MOF structures to improve the gas detection by SERS spectra but also enriches the understanding of the microcosmic process of gaseous molecules in the mixed gas environment to optimize MOF structures for gas capture and storage.

Investigation of organic monoradicals reactivity using surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) and self-assembled monolayer (SAM) approaches were used to investigate the reactions of organic monoradicals with methanol. An attempt was made to generate monoradicals from thiophenols and phenylmethanethiols substituted with bromine, iodine, and nitro groups by irradiation with UV light. Monolayers of radical precursors were deposited on SERS substrates, which were then immersed in methanol and irradiated for 1 and/or 3, 6, 12 and 24 h in a UV photochemical reactor. Pre- and postreaction SERS spectra were obtained by using a confocal Raman microscope and compared with the spectra of expected products of the radical reaction with methanol. Our studies have shown that the efficiency of monoradical generation is highly dependent on the chemical structure of the precursor. In addition, it is shown that both the SERS substrate and experimental conditions used strongly influence the obtained results.

Signal-On and Highly Sensitive Electrochemiluminescence Biosensor for Hydrogen Sulfide in Joint Fluid Based on Silver-Ion-Mediated Base Pairs and Hybridization Chain Reaction

Hydrogen sulfide (H2S) in joint fluid acts as a signal molecule to regulate joint inflammation. Direct detection of H2S in joint fluid is of great significance for the diagnosis and treatment of arthritis. However, due to the low volume of joint fluid and low H2S concentration, existing methods face the problem of the insufficient limit of detection. In this study, a highly sensitive biosensor was proposed by designing a primer probe and combining it with hybrid chain reaction (HCR) under the strong interaction between metal ions and H2S to achieve H2S detection. The primer probe containing multiple cytosine (C) sequences was fixed on a gold electrode, and the C–Ag–C hairpin structure was formed under the action of Ag+. In the presence of H2S, it can combine with Ag+ in the hairpin structure to form Ag2S, which leads to the opening of the hairpin structure and triggers the hybridization chain reaction (HCR) with another two hairpin structures (H1 and H2). A large number of double-stranded nucleic acid structures can be obtained on the electrode surface. Finally, Ru(phen)32+ can be embedded into the double chain structure to generate the electrochemiluminescence (ECL) signal. The linear response of the H2S biosensor ranged from 0.1000 to 1500 nM, and the limit of detection concentration of H2S was 0.0398 nM. The developed biosensor was successfully used to determine H2S in joint fluid.

Fe-doped MOF-derived N-rich porous carbon nanoframe for H2 S cataluminescence sensing

Metal-doped porous carbon matrix composites are considered as outstanding H₂ S cataluminescence sensing materials for their good sulfur tolerance and high cataluminescence activity. In this work, Fe-doped MOF-derived N-rich porous carbon nanoframe was successfully fabricated by pyrolysis of Fe-doped ZIF-8 in an Ar atmosphere at a temperature of 900 °C, and used for H₂ S cataluminescence sensing. Along with zinc volatilization, the obtained porous carbon nanoframe not only had high specific surface area and abundant voids, but also had well dispersed Fe species doped in the skeleton. Compared with Fe₂ O₃ /ZnO composites derived from the same precursor but different pyrolysis terms, this as-prepared Fe-doped N-rich porous carbon presented three times increase of cataluminescence intensity towards H₂ S, attributing to the porous carbon skeleton which is indispensable for dispersing catalytic active sites and providing more absorptive surface and voids. Comparably, this proposed sensor demonstrated high sensitivity and good selectivity, with the detection range of 1.57-19.58 μg·mL^-1 and detection limit as 0.13 μg·mL^-1 towards H₂ S. This work may provide a new pathway for preparing catalysts for cataluminescence sensing with better metal distribution, higher specific surface area, richer pores than ever before.

Accurate Tumor Subtype Detection with Raman Spectroscopy via Variational Autoencoder and Machine Learning

Accurate diagnosis of cancer subtypes is a great guide for the development of surgical plans and prognosis in the clinic. Raman spectroscopy, combined with the machine learning algorithm, has been demonstrated to be a powerful tool for tumor identification. However, the analysis and classification of Raman spectra for biological samples with complex compositions are still challenges. In addition, the signal-to-noise ratio of the spectra also influences the accuracy of the classification. Herein, we applied the variational autoencoder (VAE) to Raman spectra for downscaling and noise reduction simultaneously. We validated the performance of the VAE algorithm at the cellular and tissue levels. VAE successfully downscaled high-dimensional Raman spectral data to two-dimensional (2D) data for three subtypes of non-small cell lung cancer cells and two subtypes of kidney cancer tissues. Gaussian naïve bayes was applied to subtype discrimination with the 2D data after VAE encoding at both the cellular and tissue levels, significantly outperforming the discrimination results using original spectra. Therefore, the analysis of Raman spectroscopy based on VAE and machine learning has great potential for rapid diagnosis of tumor subtypes.

In Situ Monitoring of Dynamic Photocatalysis of Metal-Organic Frameworks by Three-Dimensional Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

Metal-organic frameworks (MOFs) are promising as novel disinfectants due to the reactive oxygen species (ROS) produced in their photocatalytic processes. The optimal MOF is screened as the best disinfectant, representing high-efficacy production of ROS under photocatalytic conditions. However, current methods to screen abundant MOFs for disinfectant application are generally semiquantitative or ex situ methods [such as electron paramagnetic resonance (EPR) measurements], so achieving a strategy that can quantitatively screen an optimal MOF in situ and is reliable is demanded. Herein, we developed a three-dimensional (3D) shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) platform to study the dynamic photocatalytic processes of various MOFs (e.g., ZIF-67, ZIF-8, and UIO-66) in situ. This platform comprises silica shell-isolated gold nanoparticles (AuNPs) modified on silicon nanowire arrays (SiNWArs). The MOF is then self-assembled on the 3D-SHINERS substrate. Using this platform, we recorded dynamic spectroscopic evidence of ROS formation by various MOFs under sunlight irradiation. By dynamic comparison, ZIF-67 has the most robust photocatalytic efficiency, ∼1.7-fold stronger than that of ZIF-8 and ∼42.6-fold stronger than that of UIO-66. As expected, ZIF-67 displays the best antibacterial ability, up to 99% in the agar plate assay. This work provides a versatile platform for dynamically monitoring photocatalytic performance and screening antibacterial MOFs.

Multicolor hydrogen sulfide sensor for meat freshness assessment based on Cu2+-modified boron nitride nanosheets-supported subnanometer gold nanoparticles

Hydrogen sulfide (H₂S) has emerged as an important indicator in the spoilage process of meat. In this study, a mimetic enzyme based on Cu²⁺-modified boron nitride nanosheets-supported gold nanoparticles (AuNPs/Cu²⁺-BNNS) was synthesized, which can be used to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The H₂S gas can inhibit the activity of AuNPs/Cu²⁺-BNNS toward catalytic oxidation of TMB. Meanwhile, the usage of headspace method could avoid most interferences in the rotten sample. Various concentrations of TMB⁺ could change the aspect ratio of the gold nanoroads (AuNRs), which results in vivid color changing and UV-vis spectra shifting. The sensor had a good linear relationship with H₂S concentration ranging from 10.0 to 90.0 μmol/L, and the detection limit is 7.8 μmol/L. The AuNPs/Cu²⁺-BNNS sensors were successfully applied to detect H₂S produced by meat spoilage with satisfying results.

CdS Micrometer Hollow Spheres for Detecting Alcohols Except Methanol with Strong Anti-interference Ability

Cadmium sulfide micrometer hollow spheres (CdS MHs) were fabricated by a hydrothermal method. The performance of the CdS MHs sensor was evaluated by detecting volatile organic compounds such as methanol, ethanol, 1-propanol, isopropanol, n-butanol, iso-butyl alcohol, iso-amyl alcohol, acetone, and xylene. It was found that the optimum working temperature of the CdS MHs sensor is 190 °C. The response of the CdS MHs can reach 27.4-100 ppm ethanol and reach 84.55-100 ppm isopropanol. Comparing the response to pure 5 ppm isopropanol (iso-amyl alcohol) with the mixture of 5 ppm isopropanol (iso-amyl alcohol) and 50 ppm acetone or 5 ppm isopropanol (iso-amyl alcohol) and 50 ppm methanol, the relative deviation was -1.33% (-7.11%) or -6.19% (9.20%). It suggested that the CdS MHs sensor had a strong anti-interference ability to methanol and acetone and is suitable for detecting alcohols except methanol. Therefore, the CdS MHs sensor had good response and is a promising alcohol detection material.