Monitoring of Endogenous Hydrogen Sulfide in Living Cells Using Surface-Enhanced Raman Scattering

Phenylboronic Acid-Functionalized Ratiometric Surface-Enhanced Raman Scattering Nanoprobe for Selective Tracking of Hg2+ and CH3Hg+ in Aqueous Media and Living Cells

The development of appropriate molecular tools to monitor different mercury speciation, especially CH3Hg+, in living organisms is attractive because its persistent accumulation and toxicity are very harmful to human health. Herein, we develop a novel activity-based ratiometric SERS nanoprobe to selectively monitor Hg2+ and CH3Hg+ in aqueous media and in vivo. In this nanoprobe, a new bifunctional Raman probe bis-s-s'-[(s)-(4-(ethylcarbamoyl)phenyl)boronic acid] (b-(s)-EPBA) was synthesized and immobilized on the surface of gold nanoparticles via a Au-S bond, in which the phenylboronic acid group was employed as the recognition unit for Hg2+ and CH3Hg+ based on the Hg-promoted transmetalation reaction. In the presence of Hg2+ and CH3Hg+, a new surface-enhanced Raman scattering (SERS) peak aroused from of C-Hg appeared at 1080 cm-1, and the SERS intensity at 1002 cm-1 belonged to the B-O symmetric stretching decreased simultaneously. The quantitative tracking of Hg2+ and CH3Hg+ was realized based on the SERS intensity ratio (I1080/I1303) with rapid response (∼4 min) and high sensitivity, with detection limits of 10.05 and 25.13 nM, respectively. Moreover, the SERS sensor was used for the quantitative detection of Hg2+ and CH3Hg+ in four actual water samples with a high accuracy and excellent recovery. More importantly, cell imaging experiments showed that AuNPs@b-(s)-EPBA could quantitatively detect intracellular CH3Hg+ and had a good concentration dependence in ratiometric SERS imaging. Meanwhile, we demonstrated that AuNPs@b-(s)-EPBA could detect and image CH3Hg+ in zebrafish. We anticipate that AuNPs@b-(s)-EPBA could potentially be used to study the physiological functions related to CH3Hg+ in the future.

Tailoring strategies of SERS tags-based sensors for cellular molecules detection and imaging

As an emerging nanoprobe, surface enhanced Raman scattering (SERS) tags hold significant promise in sensing and bioimaging applications due to their attractive merits of anti-photobleaching ability, high sensitivity and specificity, multiplex, and low background capabilities. Recently, several reviews have proposed the application of SERS tags in different fields, however, the specific sensing strategies of SERS tags-based sensors for cellular molecules have not yet been systematically summarized. To provide beneficial and comprehensive insights into the advanced SERS tags technique at the cellular level, this review systematically elaborated on the latest advances in SERS tags-based sensors for cellular molecules detection and imaging. The general SERS tags-based sensing strategies for biomolecules and ions were first introduced according to molecular classes. Then, aiming at such molecules located in the extracellular, cellular membrane and intracellular regions, the tailored strategies by designing and manipulating SERS tags were summarized and explored through several key examples. Finally, the challenges and perspectives of developing high performance of advanced SERS tags were briefly discussed to provide effective guidance for further development and extended applications.

Hierarchical PVDF/ZnO/Ag/ZIF-8 nanofiber membrane used in trace-level Raman detection of H2S

surface enhanced Raman scattering (SERS) detection of gases has always been difficult due to the low affinity and poor Raman cross section of the moving molecules. To mitigate the impact of these problems on detection of gases, a structure of zinc oxide/silver nanowires coated with zeolitic imidazolate framework-8 (ZnO NWs/Ag/ZIF-8) was constructed on polyvinylidene fluoride (PVDF) nanofiber membrane (PVDF/ZnO NWs/Ag/ZIF-8) and in detail researched in this work. Benefitting from the quadruple synergistic effect of efficient Knudsen diffusion of gas molecules inside ZIF-8, enrichment of ZIF-8 microsponges for gaseous molecules, regulation of ZIF-8 dielectric layer for light and reverse light scattering of ZnO NW/Ag tip, the structure was proven to have precise co-confinement on both hot spots and gaseous molecules. As a result, this PVDF/ZnO NWs/Ag/ZIF-8 achieved excellent detection for hydrogen sulfide (H2S), with a limit of detection of 1 × 10-10 v/v and the minimum relative standard deviation value of ca. 7.13 %. Furthermore, as a proof of concept, in practical application, we designed and assembled our substrate (3.5 cm × 3.5 cm) into a SERS face mask and realized efficient monitoring of H2S in human's exhaled breath.

Surface-Enhanced Raman Spectroscopy: Current Understanding, Challenges, and Opportunities

While surface-enhanced Raman spectroscopy (SERS) has experienced substantial advancements since its discovery in the 1970s, it is an opportunity to celebrate achievements, consider ongoing endeavors, and anticipate the future trajectory of SERS. In this perspective, we encapsulate the latest breakthroughs in comprehending the electromagnetic enhancement mechanisms of SERS, and revisit CT mechanisms of semiconductors. We then summarize the strategies to improve sensitivity, selectivity, and reliability. After addressing experimental advancements, we comprehensively survey the progress on spectrum-structure correlation of SERS showcasing their important role in promoting SERS development. Finally, we anticipate forthcoming directions and opportunities, especially in deepening our insights into chemical or biological processes and establishing a clear spectrum-structure correlation.

Cell membrane-targeted surface enhanced Raman scattering nanoprobes for the monitoring of hydrogen sulfide secreted from living cells

Hydrogen sulfide (H2S), an important gas signal molecule, participates in intercellular signal transmission and plays a considerable role in physiology and pathology. However, in-situ monitoring of H2S level during the processes of material transport between cells remains considerably challenging. Herein, a cell membrane-targeted surface-enhanced Raman scattering (SERS) nanoprobe was designed to quantitatively detect H2S secreted from living cells. The nanoprobes were fabricated by assembling cholesterol-functionalized DNA strands and dithiobis(phenylazide) (DTBPA) molecules on core-shell gold nanostars embedded with 4-mercaptoacetonitrile (4-MBN) (AuNPs@4-MBN@Au). Thus, three functions including cell-membrane targeted via cholesterol, internal standard calibration, and responsiveness to H2S through reduction of azide group in DTBPA molecules were integrated into the nanoprobes. In addition, the nanoprobes can quickly respond to H2S within 90 s and sensitively, selectively, and reliably detect H2S with a limit of detection as low as 37 nM due to internal standard-assisted calibration and reaction specificity. Moreover, the nanoprobes can effectively target on cell membrane and realize SERS visualization of dynamic H2S released from HeLa cells. By employing the proposed approach, an intriguing phenomenon was observed: the other two major endogenous gas transmitters, carbon monoxide (CO) and nitric oxide (NO), exhibited opposite effect on H2S production in living cells stimulated by related gas release molecules. In particular, the introduction of CO inhibited the generation of H2S in HeLa cells, while NO promoted its output. Thus, the nanoprobes can provide a robust method for investigating H2S-related extracellular metabolism and intercellular signaling transmission.

Block copolymer-templated surface-enhanced Raman scattering-active nanofibers for hydrogen sulfide detection

Metabolic disorders involving endogenous H2S have been linked to a variety of serious human diseases, particularly cancer. In this study, we employed nanofibers with surface-enhanced Raman scattering (SERS) activity for the detection of H2S within live cells. These nanofibers were chosen for their minimal invasiveness, high spatial resolution, and enhanced SERS sensitivity. To improve the performance of SERS, highly sensitive core-shell multibranched-Au NPs (MBAuNP)@Ag NPs were decorated on the nanofibers as SERS tags for H2S detection. A SERS probe named MBN, embedded between the Au core and Ag shell, was utilized for quantitative detection. These nanofibers exhibited excellent reproducibility (relative standard deviation (RSD) within 5.7 %) and demonstrated a strong linear relationship with sulfide concentrations ranging from 50 nM to 1 μM, with an estimated detection limit of 0.12 nM. As a proof of concept, the aforementioned nanofibers were successfully applied to detect endogenous H2S in living cells, offering a potential analytical method in the related research of detection.

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.

Responsive luminescent silver-based metal-organic frameworks for highly sensitive and selective detection of hydrogen sulfide in biological system via a self-assembled headspace separation device

As a highly toxic gas pollutant and also an endogenous gaseous signaling molecule existing in a variety of physiological processes, the rapid and accurate in-field detection of hydrogen sulfide is of great concern. Nevertheless, two drawbacks as for the optical probes for H2S detection, taking about a long time to reach the optical signal balance or the low selectivity, always exist. Herein, by using a highly photoluminescent and H2S-stimuli responsive silver-based metal-organic frameworks (MOFs): Ag-BDC (BDC = 1, 4-benzene dicarboxylate), we demonstrated that the luminescence intensity of Ag-BDC MOFs was inversely proportional to the concentration of H2S due to the Ag-S coordination and the obstruction of ligand-to-metal charge transfer (LMCT) transition process, and there was a quick response time of below 3.0 min. Combined with a simple customized device to separate H2S from the sample, the selectivity of the method for H2S detection could be greatly improved, and no interference would be caused even if the other sulfur-containing species coexisted. The luminescence probe presented a favorable sensitivity within a linear range of 0.1-1000 μM along with a detection limit of 23.7 nM. When employed to assay the endogenous sulfide level in the human serum and mouse brain tissue, the approach showed recoveries from 96.3% to 102% with relative standard derivation (RSD) less than 2.0%. By the integration of the responsive luminescent silver-based MOFs with a simple self-assembled headspace separation device, obviously the present strategy could be beneficial to the development and design of the in-field fast H2S measurement, possessing particular advantages in biological systems to eliminate the potential interferences.

A 'Frugal' EGFET Sensor for Waterborne H2S

Hydrogen sulphide (H2S) is a toxic gas soluble in water, H2Saq, as a weak acid. Since H2Saq usually originates from the decomposition of faecal matter, its presence also indicates sewage dumping and possible parallel waterborne pathogens associated with sewage. We here present a low footprint ('frugal') H2Saq sensor as an accessible resource for water quality monitoring. As a sensing mechanism, we find the chemical affinity of thiols to gold (Au) translates to H2Saq. When an Au electrode is used as a control gate (CG) or floating gate (FG) electrode in the electric double layer (EDL) pool of an extended gate field effect transistor (EGFET) sensor, EGFET transfer characteristics shift along the CG voltage axis in response to H2Saq. We rationalise this by the interface potential from the adsorption of polar H2S molecules to the electrode. The sign of the shift changes between Au CG and Au FG, and cancels when both electrodes are Au. The sensor is selective for H2Saq over the components of urine, nor does urine suppress the sensor's ability to detect H2Saq. Electrodes can be recovered for repeated use by washing in 1M HCl. Quantitatively, CG voltage shift is fitted by a Langmuir-Freundlich (LF) model, supporting dipole adsorption over an ionic (Nernstian) response mechanism. We find a limit-of-detection of 14.9 nM, 100 times below potability.

Electric Field Promoted Click Surface-Enhanced Raman Spectroscopy for Rapid and Specific Detection of DNA 2-Deoxyribose 5'-Aldehyde Oxidation Products in Plasma

Rapid identification of DNA oxidative damage sites is of great significance for disease diagnosis. In this work, electric field-regulated click reaction surface-enhanced Raman spectroscopy (e-Click-SERS) was developed aiming at the rapid and specific analysis of furfural, the biomarker of oxidative damage to the 5-carbon site of DNA deoxyribose. In e-Click-SERS, cysteamine-modified porous Ag filaments (cys@p-Ag) were prepared and used as electrodes, amine-aldehyde click reaction sites, and SERS substrates. Cysteamine was controlled as an "end-on" conformation by setting the voltage of cys@p-Ag at -0.1 V, which ensures its activity in participating in the amine-aldehyde click reaction during the detection of furfural. Benefiting from this, the proposed e-Click-SERS method was found to be sensitive, rapid-responding, and interference-resistant in analyzing furfural from plasma. The method detection limits of furfural were 5 ng mL-1 in plasma, and the whole "extraction and detection" procedure was completed within 30 min with satisfactory recovery. Interference from 13 kinds of common plasma metabolites was investigated and found to not interfere with the analysis, according to the exclusive adaptation of the amine-aldehyde click reaction. Notably, the e-Click-SERS technique allows in situ analysis of biological samples, which offers great potential to be a point-of-care testing tool for detecting DNA oxidative damage.

Smart Nanoplatform for Visualizing Hydrogen Sulfide and Amplifying Oxidative Stress to Tumor Apoptosis

Oxidative stress is involved in various signaling pathways and serves a key role in inducing cell apoptosis. Therefore, it is significant to monitor oxidative stress upon drug release for the assessment of therapeutic effects in cancer cells. Herein, a glutathione (GSH)-responsive surface-enhanced Raman scattering (SERS) nanoplatform is proposed for ultra-sensitively monitoring the substance related with oxidative stress (hydrogen sulfide, H2S), depleting reactive sulfur species and releasing anticancer drugs to amplify oxidative stress for tumor apoptosis. The Au@Raman reporter@Ag (Au@M@Ag) nanoparticles, where a 4-mercaptobenzonitrile molecule as a Raman reporter was embedded between layers of gold and silver to obtain sensitive SERS response, were coated with a covalent organic framework (COF) shell to form a core-shell structure (Au@M@Ag@COFs) as the SERS nanoplatform. The COF shell loading doxorubicin (DOX) of Au@M@Ag@COFs exhibited the GSH-responsive degradation capacity to release DOX, and its Ag layer as the sensing agent was oxidized to Ag2S by H2S to result in its prominent changes in SERS signals with a low detection limit of 0.33 nM. Moreover, the releasing DOX can inhibit the generation of H2S to promote the production of reactive oxygen species, and the depletion of reactive sulfur species (GSH and H2S) in cancer cells can further enhance the oxidative stress to induce tumor apoptosis. Overall, the SERS strategy could provide a powerful tool to monitor the dynamic changes of oxidative stress during therapeutic processes in a tumor microenvironment.

Identification and Detection of Intracellular Reactive Sulfur Species Using a Reaction-Mediated Dual-Recognition Strategy

Reactive sulfur species (RSS) are emerging as a potential key gasotransmitter in diverse physiological processes linking two signaling molecules H2S and SO2. However, the exact roles of H2S and SO2 remain unclear. A major hurdle is the shortage of accurate and robust approaches for sensing of H2S and SO2 in biological systems. Herein, we report a reaction-mediated dual-recognition strategy-based nanosensor, silver nanoparticles (AgNPs)-loaded MIL-101 (Fe) (ALM) hybrids, for the simultaneous detection of H2S and SO2 in a living cell. Upon exposure to H2S, AgNPs can be oxidized to form Ag2S, causing a decrease of surface enhanced Raman spectroscopy (SERS) signals of p,p'-dimercaptoazobenzene. Moreover, SO2 reacts with the amino moiety of MIL-101 to form charge-transfer complexes, resulting in an increment of fluorescent (FL) intensity. The ALM with dual-modal signals can simultaneously analyze H2S and SO2 at a concentration as low as 2.8 × 10-6 and 0.003 μM, respectively. Most importantly, the ALM sensing platform enables targeting mitochondria and detection multiple RSS simultaneously in living cells under external stimulation, as well as displays indiscernible crosstalk between SERS and FL signals, which is very beneficial for the comprehension of physiological issues related with RSS.

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.

Facile fabrication of laser induced versatile graphene-metal nanoparticles electrodes for the detection of hazardous molecules

In this work, we developed a facile method to fabricate laser induced versatile graphene-metal nanoparticles (LIG-MNPs) electrodes with redox molecules sensing capabilities. Unlike conventional post-electrodes deposition, versatile graphene-based composites were engraved by a facile synthesis process. As a general protocol, we successfully prepared modular electrodes including LIG-PtNPs and LIG-AuNPs and applied them to electrochemical sensing. This facile laser engraving process enables rapid preparation and modification of electrodes, as well as simple replacement of metal particles modification towards varied sensing targets. The LIG-MNPs showed high sensitivity towards H₂O₂ and H₂S due to their excellent electron transmission efficiency and electrocatalytic activity. By simply changing the types of coated precursors, the LIG-MNPs electrodes have successfully achieved real-time monitoring of H₂O₂ released from tumor cells and H₂S contained in wastewater. This work contributed a universal and versatile protocol for quantitatively detecting a wide range of hazardous redox molecules.

Review of Chemical Sensors for Hydrogen Sulfide Detection in Organisms and Living Cells

As the third gasotransmitter, hydrogen sulfide (H₂S) is involved in a variety of physiological and pathological processes wherein abnormal levels of H₂S indicate various diseases. Therefore, an efficient and reliable monitoring of H₂S concentration in organisms and living cells is of great significance. Of diverse detection technologies, electrochemical sensors possess the unique advantages of miniaturization, fast detection, and high sensitivity, while the fluorescent and colorimetric ones exhibit exclusive visualization. All these chemical sensors are expected to be leveraged for H₂S detection in organisms and living cells, thus offering promising options for wearable devices. In this paper, the chemical sensors used to detect H₂S in the last 10 years are reviewed based on the different properties (metal affinity, reducibility, and nucleophilicity) of H₂S, simultaneously summarizing the detection materials, methods, linear range, detection limits, selectivity, etc. Meanwhile, the existing problems of such sensors and possible solutions are put forward. This review indicates that these types of chemical sensors competently serve as specific, accurate, highly selective, and sensitive sensor platforms for H₂S detection in organisms and living cells.

Cu2O/Co3O4 nanoarrays for rapid quantitative analysis of hydrogen sulfide in blood

2D heterostructure nanoarrays have emerged as a promising sensing material for rapid disease detection applications. In this study, a bio-H₂S sensor based on Cu₂O/Co₃O₄ nanoarrays was proposed, the controllable preparation of the nanoarrays being achieved by exploring the experimental parameters of the 2D electrodeposition in situ assembly process. The nanoarrays were designed as a multi-barrier system with strict periodicity and long-range order. Based on the interfacial conductance modulation and vulcanization reaction of Cu₂O and Co₃O₄, the sensor exhibited superior sensitivity, selectivity, and stability to H₂S in human blood. In addition, the sensor exhibited a reasonable response to 0.1 μmol L^-1 Na₂S solution, indicating that it had a low detection limit for practical applications. Moreover, first-principles calculations were performed to study changes in the heterointerface during the sensing process and the mechanism of rapid response of the sensor. This work demonstrated the reliability of Cu₂O/Co₃O₄ nanoarrays applied in portable sensors for the rapid detection of bio-H₂S.

Wearable SERS Sensor Based on Omnidirectional Plasmonic Nanovoids Array with Ultra-High Sensitivity and Stability

Surface-enhanced Raman spectroscopy (SERS) is a promising technology for wearable sensors due to its fingerprint spectrum and high detection sensitivity. However, since SERS-activity is sensitive to both the distribution of "hotspots" and excitation angle, it is profoundly challenging to develop a wearable SERS sensor with high stability under various deformations during movements. Herein, inspired by omnidirectional light-harvesting of the compound eye of Xenos Peckii, a wearable SERS sensor is developed using omnidirectional plasmonic nanovoids array (OPNA), which is prepared by assembling a monolayer of metal nanoparticles into the artificial plasmonic compound-eye (APC). Specifically, APC is an interconnected frame containing omnidirectional "pockets" and acts as an "armour", not only rendering a broadband and omnidirectional enhancement of "hotspots" in the delicate nanoparticles array, but also maintaining an integrity of the "hotspots" against external mechanical deformations. Furthermore, an asymmetry super-hydrophilic pattern is fabricated on the surface of OPNA, endowing the hydrophobic OPNA with the ability to spontaneously extract and concentrate the analytes from sweat. Such an armored SERS sensor can enable the wearable and in situ analysis with high sensitivity and stability, exhibiting great potential in point-of-care analysis.

In Situ Identification of Unknown Crystals in Acute Kidney Injury Using Raman Spectroscopy

Raman spectroscopy is a well-established and powerful tool for in situ biomolecular evaluation. Type 2 crystal nephropathies are characterized by the deposition of crystalline materials in the tubular lumen, resulting in rapid onset of acute kidney injury without specific symptoms. Timely crystal identification is essential for its diagnosis, mechanism exploration and therapy, but remains challenging. This study aims to develop a Raman spectroscopy-based method to assist pathological diagnosis of type 2 crystal nephropathies. Unknown crystals in renal tissue slides from a victim suffered extensive burn injury were detected by Raman spectroscopy, and the inclusion of crystals was determined by comparing Raman data with established database. Multiple crystals were scanned to verify the reproducibility of crystal in situ. Raman data of 20 random crystals were obtained, and the distribution and uniformity of substances in crystals were investigated by Raman imaging. A mouse model was established to mimic the crystal nephropathy to verify the availability of Raman spectroscopy in frozen biopsy. All crystals on the human slides were identified to be calcium oxalate dihydrate, and the distribution and content of calcium oxalate dihydrate on a single crystal were uneven. Raman spectroscopy was further validated to be available in identification of calcium oxalate dihydrate crystals in the biopsy specimens. Here, a Raman spectroscopy-based method for in situ identification of unknown crystals in both paraffin-embedded tissues and biopsy specimens was established, providing an effective and promising method to analyze unknown crystals in tissues and assist the precise pathological diagnosis in both clinical and forensic medicine.

1,4-Benzenedithiol-Bridged Nanogap-Based Individual Particle Surface-Enhanced Raman Spectroscopy Mechanical Probe for Revealing the Endocytic Force

1,4-Benzenedithiol (BDT)-bridged core-satellite assemblies, as surface-enhanced Raman spectroscopy (SERS) mechanical probes, can be employed for real-time monitoring of the dynamics of endocytic forces and the accompanying trajectory of nanoparticles during the endocytosis process. These mechanical probes exhibit good responses in terms of SERS intensity ratios while undergoing mechanical pressure. Force tracing and the accompanying trajectory of nanoparticles are resolved accurately to render the endocytosis process in live cells. Density functional theory simulation results further proved the sensing scheme due to the electrons transforming between BDT and gold nanoparticles. Furthermore, this SERS mechanical probe is a valid method to visualize endocytic forces at multiple locations and establish a direct criterion to discriminate between cancer cells and normal cells.

A Rational Designed Bioorthogonal Surface-Enhanced Raman Scattering Nanoprobe for Quantitatively Visualizing Endogenous Hydrogen Sulfide in Single Living Cells

Understanding the biology of gasotransmitters in living cells is of significance but remains challenging due to largely a lack of robust molecular probes. Here, we present the facile design and synthesis of a bioorthogonal Raman probe, 4-azidobenzenethiol (4-ABT), for endogenous hydrogen sulfide (H₂S) imaging in single live cells by surface-enhanced Raman scattering (SERS). 4-ABT bears a thiol group and an azido group in the benzene ring, thus affording a bifunction to firmly bind to the gold nanoparticle surface and specifically respond to H₂S. Moreover, the 4-ABT-based SERS nanoprobe shows a dose-dependent spectral change in the cellular Raman-silent region upon reacting with H₂S, allowing ratiometric quantitative detection and visualization of intracellular H₂S status without bio-interference. The ease of fabrication and superior performance of the novel SERS nanoprobe demonstrate its promising application in studies of H₂S-related signaling networks.

Metal coordination induced SERS nanoprobe for sensitive and selective detection of histamine in serum

Sensitivity and credibility detecting histamine (HA) as an important neurotransmitter in biofluids is of importance in analytical science and physiology. Surface-enhanced Raman spectroscopy (SERS) is able to realize the high sensitivity with single molecules level, but providing the high sensitivity for HA with a small cross section remains a challenge. Here we develop the metal complex-based SERS nanoprobe nitrilotriacetic acid-Ni²⁺ (NTA-Ni²⁺) combined with self-assemble Au NPs active substrates for sensitive detection of HA. The NTA-Ni²⁺ can capture the HA molecules close to Au NPs substrates and then amplify the Raman signals of HA owing to the formation of a complex of NTA-Ni²⁺-HA. The self-assemble Au film through the evaporation-driven method can provide the high-density hot spots substrate with high stability and reproducibility. The NTA-Ni²⁺ decorated Au NPs as nanoprobe responds to HA with 1 μM level of sensitivity. More importantly, the developed SERS nanoprobe composing of NTA-Ni²⁺ and self-assemble Au NPs can be utilized to detect and monitor the HA spiked into serum, indicating the potential prospect in analysis of HA in complex specimen.

Sensitivity and Selectivity Analysis of Fluorescent Probes for Hydrogen Sulfide Detection

Hydrogen sulfide (H₂S) is a gasotransmitter known to regulate physiological and pathological processes. Abnormal H₂S levels have been associated with a range of conditions, including Parkinson's and Alzheimer's diseases, cardiovascular and renal diseases, bacterial and viral infections, as well as cancer. Therefore, fast and sensitive H₂S detection is of significant clinical importance. Fluorescent H₂S probes hold great potential among the currently developed detection methods because of their high sensitivity, selectivity, and biocompatibility. However, many proposed probes do not provide a gold standard for proper use and selection. Consequently, issues arise when applying the probes in different conditions. Therefore, we systematically evaluated four commercially available probes (WSP‐1, WSP‐5, CAY, and P3), considering their detection range, sensitivity, selectivity, and performance in different environments. Furthermore, their capacity for endogenous H₂S imaging in live cells was demonstrated.

In Situ Detection of Hydrogen Sulfide in 3D-Cultured, Live Prostate Cancer Cells Using a Paper-Integrated Analytical Device

In this study, a paper-integrated analytical device that combined a paper-based colorimetric assay with a paper-based cell culture platform was developed for the in situ detection of hydrogen sulfide (H2S) in three-dimensional (3D)-cultured, live prostate cancer cells. Two kinds of paper substrates were fabricated using a simple wax-printing methodology to form the cell culture and detection zones, respectively. LNCaP cells were seeded directly on the paper substrate and grown in the paper-integrated analytical device. The cell viability and H2S production of LNCaP cells were assessed using a simple water-soluble tetrazolium salt colorimetric assay and H2S-sensing paper, respectively. The H2S-sensing paper showed good sensitivity (sensitivity: 6.12 blue channel intensity/μM H2S, R2 = 0.994) and a limit of quantification of 1.08 μM. As a result, we successfully measured changes in endogenous H2S production in 3D-cultured, live LNCaP cells within the paper-integrated analytical device while varying the duration of incubation and substrate concentration (L-cysteine). This paper-integrated analytical device can provide a simple and effective method to investigate H2S signaling pathways and drug screening in a 3D culture model.

Near-Infrared-II Bioimaging for in Vivo Quantitative Analysis

Near-Infrared-II (NIR-II) bioimaging is a newly emerging visualization modality in real-time investigations of biological processes research. Owning to advances in reducing photon scattering and low tissue autofluorescence levels in NIR-II region (1,000-1700 nm), NIR-II bioimaging affords high resolution with increasing tissue penetration depth, and it shows greater application potential for in vivo detection to obtain more detailed qualitative and quantitative parameters. Herein, this review summarizes recent progresses made on NIR-II bioimaging for quantitative analysis. These emergences of various NIR-II fluorescence, photoacoustic (PA), luminescence lifetime imaging probes and their quantitative analysis applications are comprehensively discussed, and perspectives on potential challenges facing in this direction are also raised.

Analytical Methods for Detection of Gasotransmitter Hydrogen Sulfide Released from Live Cells

Hydrogen sulfide (H₂S) plays an important role in mammals as a signaling molecule. Recently, abnormal H₂S concentration has been associated with several pathophysiological states, such as diabetes mellitus, hypertension, Alzheimer's disease, and Parkinson's disease. As regulating H₂S concentration can be a very prominent way of developing new drugs, many researchers have paid great attention to H₂S research. To understand the role of H₂S in pathophysiology and develop H₂S-based therapies, it is necessary to measure the exact concentration of H₂S within biological systems. But, H₂S is volatile and can be easily oxidized. Besides, the active sites for several biological effects of H₂S are inside the cell. Therefore, there is a need for the development of new methods for the accurate and reliable detection of H₂S within live cells. This review provides a summary of recent developments in H₂S detection methods for live cell analysis.

In Situ Activatable Ratiometric NIR-II Fluorescence Nanoprobe for Quantitative Detection of H2S in Colon Cancer

As key characteristic molecules, several H₂S-activated probes have been explored for colon cancer studies. However, a few ratiometric fluorescence (FL) probes with NIR-II emissions have been reported for the quantitative detection of H₂S in colon cancer in vivo. Here, we developed an in situ H₂S-activatable ratiometric nanoprobe with two NIR-II emission signals for the detection of H₂S and intelligently lighting up colon cancer. The nanoprobe comprised a down conversion nanoparticle (DCNP), which emitted NIR-II FL at 1550 nm on irradiation with a 980 nm laser (F_{1550Em, 980Ex}). Further, human serum albumin (HSA) was combined with Ag⁺ on the surface of DCNP to form a DCNP@HSA-Ag⁺ nanoprobe. In the presence of H₂S, Ag₂S quantum dots (QDs) were formed in coated HSA, which emitted FL at approximately 1050 nm on irradiation with an 808 nm laser (F_{1050Em, 808Ex}) through an H₂S-induced chemical reaction between H₂S and Ag⁺; however, the FL signal of DCNP was stable at 1550 nm (F_{1550Em, 980Ex}), generating a H₂S concentration-dependent ratiometric F_{1050Em, 808Ex}/F_{1550Em, 980Ex} signal. The NIR-II ratiometric nanoprobe was successfully used for the accurate quantitative detection of H₂S and the detection of the precise location of colon cancer through an endogenous H₂S-induced in situ reduction reaction to form Ag₂S QDs. Thus, these findings provide a new strategy for the specific detection of targeted molecules and diagnosis of disease based on the in situ-activatable NIR-II ratiometric FL nanoprobe.

A target-triggered and self-calibration aptasensor based on SERS for precise detection of a prostate cancer biomarker in human blood

Sensitive and precise detection of prostate-specific antigen (PSA) is critical for prostate cancer screening and monitoring. Herein, a target-triggered and self-calibration aptasensor based on a core-satellite nanostructure using surface-enhanced Raman spectroscopy (SERS) technology was developed for the sensitive and reliable determination of PSA protein, with a limit of detection of 0.38 ag mL-1 and a dynamic detection range of 10-2 to 10-15 mg mL-1. Furthermore, the proposed approach for the detection of PSA in patient blood samples was performed, and results showed that it is capable of providing comparable detection accuracy associated with a larger dynamic detection range and a lower detection limit as well as less sample requirement (only 5 μL) in comparison with the clinical commonly used method. Therefore, this SERS-based aptasensor for the detection of PSA in human blood samples has promising potential to be an alternative tool for clinical application in the accurate screening of prostate cancer.

Electroactive Cu2O nanocubes engineered electrochemical sensor for H2S detection

An electrochemical sensor was proposed for the detection of hydrogen sulfide (H₂S) at room temperature, by using electroactive Cu₂O nanocubes (NCs) as an electrochemical beacon. Electroactive Cu₂O NCs were synthesized on the surface of reduced graphene oxide (rGO)/Fe₃O₄ nanosheets (NSs) due to the good electronic conductivity and well-responded magnetic responses. The fabricated rGO/Fe₃O₄/Cu₂O NSs not only showed electrochemical oxidization peak at -0.1 V from Cu₂O NCs, and could be served as sensitive electrochemical beacon for the simple modification on magnetic electrodes in the applications. The unique redox reaction between Cu₂O NCs and H₂S enabled the transformation of Cu₂O NCs to Cu₉S₈ NCs, resulting in decreased electroxidation responses at -0.1 V. The constructed electrochemical platform had a limit of detection (LOD) of 230 pM and a detection range of 500 pM-100 μM. The simple and cheap electrochemical sensor developed in this paper showed potential application for H₂S detection.

Recent progress of surface-enhanced Raman spectroscopy for subcellular compartment analysis

Organelles are involved in many cell life activities, and their metabolic or functional disorders are closely related to apoptosis, neurodegenerative diseases, cardiovascular diseases, and the development and metastasis of cancers. The explorations of subcellular structures, microenvironments, and their abnormal conditions are conducive to a deeper understanding of many pathological mechanisms, which are expected to achieve the early diagnosis and the effective therapy of diseases. Organelles are also the targeted locations of drugs, and they play significant roles in many targeting therapeutic strategies. Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical tool that can provide the molecular fingerprint information of subcellular compartments and the real-time cellular dynamics in a non-invasive and non-destructive way. This review aims to summarize the recent advances of SERS studies on subcellular compartments, including five parts. The introductions of SERS and subcellular compartments are given. SERS is promising in subcellular compartment studies due to its molecular specificity and high sensitivity, and both of which highly match the high demands of cellular/subcellular investigations. Intracellular SERS is mainly cataloged as the labeling and label-free methods. For subcellular targeted detections and therapies, how to internalize plasmonic nanoparticles or nanostructure in the target locations is a key point. The subcellular compartment SERS detections, SERS measurements of isolated organelles, investigations of therapeutic mechanisms from subcellular compartments and microenvironments, and integration of SERS diagnosis and treatment are sequentially presented. A perspective view of the subcellular SERS studies is discussed from six aspects. This review provides a comprehensive overview of SERS applications in subcellular compartment researches, which will be a useful reference for designing the SERS-involved therapeutic systems.

Stimuli-Responsive Plasmonic Assemblies and Their Biomedical Applications

Among the diverse development of stimuli-responsive assemblies, plasmonic nanoparticle (NP) assemblies functionalized with responsive molecules are of a major interest. In this review, we outline a comprehensive and up-to-date overview of recently reported studies on in vitro and in vivo assembly/disassembly and biomedical applications of plasmonic NPs, wherein stimuli such as enzymes, light, pH, redox potential, temperature, metal ions, magnetic or electric field, and/or multi-stimuli were involved. Stimuli-responsive assemblies have been applied in various biomedical fields including biosensors, surfaced-enhanced Raman scattering (SERS), photoacoustic (PA) imaging, multimodal imaging, photo-activated therapy, enhanced X-ray therapy, drug release, stimuli-responsive aggregation-induced cancer therapy, and so on. The perspectives on the use of stimuli-responsive plasmonic assemblies are discussed by addressing future scientific challenges involving assembly/disassembly strategies and applications.

Cost-effective diagnostic kits for selective detection of gaseous H2S

Unsymmetrical tri-functionalized perylene diimide dyes were explored for making solution- and solid-state-based colorimetric kits for the detection of gaseous and aqueous H2S.

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

Mostly, surface-enhanced Raman scattering (SERS) sensors used the Raman characteristic bands concentrated in the Raman "fingerprint" region (500-1800 cm^-1), which may result in spectral overlapping interference. The study of the response in the Raman-silent region (10-500 and 1800-2800 cm^-1) can help overcome this problem. Hydrogen sulfide (H₂S) gas causes a great threat to human's health, but its low concentration in the airborne species is a challenge for sensitive and selective detection. Herein, a novel low-wavenumber (10-500 cm^-1) SERS sensor for H₂S gas detection has been developed based on gold nano-bipyramids (Au NBPs) encapsulated by zeolitic imidazolate framework-8 (ZIF-8) (Au NBPs@ZIF-8). The sensor takes advantage of the high adsorption capacity of ZIF-8 toward H₂S gas and the H₂S-triggered SERS spectral changes in the low-wavenumber Raman-silent region. A clear SERS peak of Au-Br at ∼175 cm^-1 generated from Au NBPs@ZIF-8 showed a decrease in the presence of H₂S because of the competition of adsorption sites between Au-S and Au-Br bonds. Furthermore, Au NBPs@ZIF-8 can enrich and monitor the level of H₂S gas with high efficiency and low interference. The developed sensor has a detection range of 0.2 nM to 20 mM with a limit of detection (LOD) of 0.17 nM. The developed sensor had been applied to detect the H₂S gas released from the spoiled fish meat with high selectivity.

Chromogenic detection of hydrogen sulfide using squarylium-based chemosensors

Squarylium-based colorimetric hydrogen sulfide (H₂S) chemosensors (SQ1, SQ2, and SQ3) were developed, and their detection properties were systematically characterized. SQ1 exhibited rapid and high resolution H₂S sensing properties through significant color changes detectable by naked-eye with limit of detection as low as 7.2 ppb. SQ1 also showed excellent selectivity for H₂S detection over other relevant anions and nucleophiles. Sensing mechanisms of SQ1 were investigated based on spectroscopic and ¹H NMR analyses with quantum calculations. Furthermore, SQ1 showed an efficient response to H2S under versatile conditions in the solution, solid, and dyed fabric states, which suggests applicability of SQ1 to simple, low-cost, and practical H₂S sensors.

Reliable Quantification of pH Variation in Live Cells Using Prussian Blue-Caged Surface-Enhanced Raman Scattering Probes

Intracellular pH is an important parameter that is highly associated with diverse physiological processes. The reliable measurement of pH values inside cells remains a formidable challenge because of the complexity of cytoplasm. Herein, we report a robust Prussian blue (PB)-caged pH-responsive surface-enhanced Raman scattering (SERS) probe for precisely mapping the dynamic pH values in live cells. The PB shell has a subnanoscale porous structure that allows only very small biospecies such as H⁺ or OH^- to pass freely through the shell and react with the encased pH-responsive SERS probe, while physically resisting the entry of large biomolecules. This probe achieved unmatched detection linearity (R² > 0.999) for pH measurements in diverse complex biological samples. Moreover, the nitrile (C≡N) in PB shows a sharp band in the cellular Raman-silent region, which serves as a background-free internal standard for accurate profiling of the probe distribution inside the cells. We applied the proposed probe to monitor the dynamic pH changes during cellular autophagy induced by different stimuli and thereby demonstrated that the PB-caged probe can reliably quantify subtle intracellular pH variations, providing an effective tool for revealing the relationship between abnormal intracellular pH and cellular functions.

Cys-functionalized AuNP substrates for improved sensing of the marine toxin STX by dynamic surface-enhanced Raman spectroscopy

Saxitoxin (STX) as one of the most harmful and typical paralytic shellfish toxins, is posing a serious threat to environmental and human health, thus it is essential to develop a sensitive and reliable analytical method for STX detection. Herein, we proposed a strategy for rapid and sensitive detection of STX with surface-enhanced Raman spectroscopy (SERS), by employing cysteine modified gold nanoparticles (Cys-AuNPs) as SERS probe to capture STX molecules through electrostatic interactions and multiple hydrogen bonds between Cys and STX molecules. Moreover, the XPS and zeta potential results indicated that Cys could bond to AuNPs through Au-S bonds and the addition of STX could induce the efficient aggregation of Cys-AuNPs owing to the presence of electrostatic interactions and multiple hydrogen bonds between Cys and STX molecules. Furthermore, considering the high sensitivity and stability of the dynamic surface-enhanced Raman spectroscopy (D-SERS) strategy with the formation of a 3D hotspot matrix, the highly sensitive detection of STX was realized to a level of 1 × 10^-7 M by using the D-SERS strategy. Consequently, Cys-AuNPs as high affinity substrates can provide high sensitivity for the detection of STX through the D-SERS strategy. Graphical abstract.

Ultrathin Hexagonal PbO Nanosheets Induced by Laser Ablation in Water for Chemically Trapping Surface-Enhanced Raman Spectroscopy Chips and Detection of Trace Gaseous H2S

Lead oxide (PbO) nanosheets are of significance in the design of functional devices. However, facile, green, and fast fabrication of ultrathin and homogenous PbO nanosheets with a chemically clean surface is still desirable. Herein, a simple and chemically clean route is developed for fabricating such nanosheets via laser ablation of a lead target in water for a short time and then ambient aging. The obtained PbO nanosheets are (002)-oriented with microsize in planar dimension and ∼15 nm in thickness. They are mostly hexagonal in shape. Experimental observations of the morphological evolution have revealed that the formation of such PbO nanosheets can be attributed to two processes: (i) laser ablation-induced formation of ultrafine Pb and PbO nanoparticles (NPs) and (ii) PbO NP aggregation and their oriented connection growth. Importantly, a composite surface-enhanced Raman spectroscopy (SERS) chip is designed and fabricated by covering a PbO nanosheet monolayer on a Au NP film. Such a composite SERS chip can be used for the fast and trace detection of gaseous H₂S in which the PbO nanosheets can effectively chemically trap H₂S molecules, demonstrating a new application of these PbO nanosheets. The response of this chip to H₂S can be detected within 10 s, and the detection limit is below 1 ppb. Also, this PbO nanosheet-based chip is reusable by heating after use. This study not only deepens the understanding of the NP-based formation mechanism of nanosheets but also provides the renewable SERS chips for the highly efficient detection of trace gaseous H₂S.

Chiral Cux OS@ZIF-8 Nanostructures for Ultrasensitive Quantification of Hydrogen Sulfide In Vivo

In this study, a Cu_x OS@ZIF-8 nanostructure is fabricated to quantify the levels of hydrogen sulfide (H₂ S) in living cells and in vivo. Zeolitic lmidazolate framework-8 (ZIF-8) is chosen as an encapsulation shell to improve the selectivity of this probe. Using this unique nanostructure, ultrasensitive quantification and bioimaging of H₂ S in living cells are successfully achieved. The lower limit of detection is 0.8 and 5.3 nmol per 10⁶ cells for circular dichroism and fluorescence modes, respectively. It is found that the chiral Cu_x OS NPs transformed into achiral Cu_x S NPs contribute to the ultrasensitive detection. Notably, this probe can also be carried out to detect and track H₂ S levels in tumor-bearing animals. The discoveries put forward for the creation of a detection platform for quantitative tracking and analysis in clinic.

Selective surface-enhanced Raman scattering detection of Tabun, VX and Cyclosarin nerve agents using 4-pyridine amide oxime functionalized gold nanopillars

We have earlier demonstrated sensitive detection of low the volatile nerve agents Tabun, Cyclosarin and VX by using handheld Raman instrumentation in conjunction with surface-enhanced Raman scattering (SERS) attained with gold and silver coated Si nanopillar substrates. In the present proof-of-concept study, the gold substrates chemically are functionalized to realize selectivity towards organophosphorus compounds (OPs) with high sensitivity. A potential capturer and reporter molecule, chemical nerve agent antidote, 4-pyridine amide oxime, is evaluated due to its high Raman cross section, high chemical affinity towards gold, and binding specificity to the target substances Tabun, VX and Cyclosarin via the oxime group. Upon selective and covalent binding, the SERS probe undergoes structural changes which are reflected in the spectral SERS responses, making it suitable for indirect monitoring of nerve agents in aqueous solution. With the probe attached to the hotspots of Au-coated Si nanopillars, the SERS signals distinctly discriminate between specific and non-specific analyte binding of Tabun, Cyclosarin and VX down to sub ppm levels. SERS spectrum of 4-PAO is measured after microliter drop coating of aqueous sample solution onto the functionalized substrates and subsequent water evaporation from surfaces. This binding assay is complemented by letting functionalized substrates being immersed into sample solutions 1 h before measuring. Binding specific SERS response decreases in following order: Tabun > VX > Cyclosarin. Overall, the concept looks promising, as expected the candidate probe 4-PAO introduces selectivity to the nanopillar gold substrates without loss of sensitivity.

Near-infrared fluorescent chemodosimeter for real-time in vivo evaluation of H2S-release efficiency of prodrug

A promising platform for evaluating H₂S-release in pharmaceutical development, and enabling a great method for monitoring H₂S in future clinical medicine.

A homogeneous photoelectrochemical hydrogen sulfide sensor based on the electronic transfer mediated by tetrasulfophthalocyanine

A homogeneous photoelectrochemical sensor for H₂S detection based on the electronic transfer mediated by [Fe(iii)PcS₄]⁺was developed with an un-modified photoelectrode.

Target-triggered hot spot dispersion for cellular biothiol detection via background-free surface-enhanced Raman scattering tags

Abnormal cellular biothiol levels are related to many abnormal physiological processes, including cancer, multidrug resistance and Alzheimer's disease, etc. In this study, the nano-aggregates of the background-free surface-enhanced Raman scattering (SERS) tags were constructed and developed for the intracellular biothiol detection via a target-triggered disaggregation process. The plasmonic nano-tags were prepared by coating gold nanoparticles with a Raman reporter (4-mercaptobenzonitrile, MBN), which exhibits a single strong peak in the cellular Raman silent region (1800-2800 cm^-1) that can eliminate the background interference of cells. Interestingly, this reporter is also the host ligand for guest mercury ions. The coordination of mercury/cyano group induce the formation of the pre-aggregates of nano-tags and the formed nano-aggregates allowing strong SERS signals of reporters. Intracellular biothiols show higher affinity to mercury ions than the SERS tags do, which can break the hot spot geometry and redisperse tags by taking away mercury ions from nano-aggregates, which dramatically decreases the SERS signals of reporters previously laid on gold nanoparticles. The developed SERS "turn off" method was used for biothiol detections in normal, cancer, drug-resistant cells, and biothiol dynamics during chemotherapy. The results demonstrate that the drug-resistant cells (MCF-ADR) lie in a higher biothiol level than cancer cells (MCF-7 and HepG2), and the normal cells (LO2) give a lower biothiol concentration compared with cancer cells. Moreover, most cancer cells are more sensitive to doxorubicin compared with the normal ones. This study provides an important strategy in learning the cellular processes that are highly associated with intracellular biothiol level.

A nitrile-mediated aptasensor for optical anti-interference detection of acetamiprid in apple juice by surface-enhanced Raman scattering

Currently, the detection of pesticide is critical for food safety assurance, but it is still challenging due to the presence of biological interferents from complex food matrix. In this study, we developed an optical anti-interference surface-enhanced Raman scattering (SERS) aptasensor system for trace detection of acetamiprid. 4-(Mercaptomethyl) benzonitrile (MMBN) containing CN bond was used as Raman tag to provide a sharp peak (2227 cm^-1) in the Raman-silent spectral window (1800-2800 cm^-1) where no Raman signal existed for most of molecules. Gold nanoparticles (AuNPs) bonded with polyadenine (polyA)-mediated aptamer and Raman tag (MMBN-AuNPs-aptamer) was synthesized as Raman probe, while the complementary DNA (cDNA) conjugated with AgNPs-decorated silicon wafer (AgNPs@Si) was used as SERS substrate. As acetamiprid molecule could specifically combine with aptamer, preventing the formation of MMBN-AuNPs-aptamer-cDNA-AgNPs@Si (expressed as "Au-AgNPs@Si") hybrid through DNA sequence linking, Raman signal intensities of MMBN in Au-AgNPs@Si decreased when the concentration of acetamiprid increased. Under the optimum assay condition, the proposed method displayed a linear response for acetamiprid detection in the range of 25-250 nM with a low detection limit of 6.8 nM. Finally, the developed aptasensor was successfully used to determine acetamiprid content in apple juice. Accordingly, this novel anti-interference SERS aptasensor could be a promising acetamiprid sensor for food safety assurance.