Simultaneous Detection of Intracellular Nitric Oxide and Peroxynitrite by a Surface-Enhanced Raman Scattering Nanosensor with Dual Reactivity

In-situ detection of peroxynitrite in a single living cell with electrochemical attosyringe

Peroxynitrite (ONOO-), a key reactive oxygen/nitrogen species, plays a crucial role in signal transduction and physiological homeostasis. However, achieving the determination of ONOO- in a single living cell remains a significant challenge. In this study, we have synthesized blue-emitting carbon dots (CDs) with a specific response to ONOO- via a simple Schiff base crosslinking strategy. The fluorescence of these CDs is efficiently quenched upon interaction with ONOO- due to a strong nitration reaction, enabling highly sensitive and selective detection of ONOO- within a concentration range of 0.06-1.0 μM, with a detection limit as low as 30 nM. Notably, we have developed an electrochemical attosyringe by loading the CDs solution into a nanopipette, facilitating in-situ detection of ONOO- in a single living cell. This approach, which differs from conventional incubation methods, offers rapid infusion and ease of operation, presenting promising opportunities for advancing single-cell analysis and enhancing our understanding of cellular microenvironments.

A dual-reactivity-based surface-enhanced Raman spectroscopy nanosensor for the simultaneous imaging of hypochlorite and nitric oxide in living cells

A surface-enhanced Raman spectroscopy (SERS) nanosensor with dual-reactivity is developed for the simultaneous imaging of hypochlorite (ClO-) and nitric oxide (NO) in living cells. Utilizing the specific reactions between functional molecules and ClO- and NO, respectively, the 2-mercapto-4-methoxy-phenol (2-MP) and o-phenylenediamine (OPD) molecules are synchronously assembled on the surface of gold nanoparticles to fabricate the dual-function nanosensors. The advantages of SERS technology, narrow peaks for spectral multiplexing and fingerprint information, further facilitate the simultaneous detection of ClO- and NO. The prepared nanosensors achieve a highly sensitive and selective measurement of ClO- and NO with a limit of detection of 0.054 μM and 0.46 μM, respectively. Furthermore, the SERS nanosensors enable the simultaneous visualization of ClO- and NO in the single living cell, which opens up the prospects to investigate the ClO-- and NO-involved physiological and pathological events.

Unraveling the structural evolution of silver plasmonic hotspots for the detection of oxidative ONOO- radicals via SERS probe decay

Peroxynitrite (ONOO-) plays a pivotal role in environmental pollution and ecosystem health, necessitating its detection for assessing ecological impacts and risks. Surface-enhanced Raman scattering (SERS) offers high sensitivity but is often limited by narrow Raman cross sections of analytes. Specialized molecules can aid SERS detection, but are complex to design and may cause nonspecific reactions in biological systems. Therefore, developing new SERS strategies is crucial for simpler, more accurate ONOO- detection. Herein, the shape instability of Ag nanomaterials in the hotspots, due to oxidation and dissolution of Ag atoms at the edges and corners, is investigated, and the detection of ONOO- is performed by SERS probes. ONOO- reacts first with the (111) facet, especially at the edges and corners. Consequently, the SERS signal of the adsorbed probe, Rhodamine 6G in hotspots can be used to monitor edge and corner dissolution that positively related to the ONOO- concentration. As a result, ONOO- concentration from 0.1 to 25 μM was detected, achieving a coefficient of determination of R2 = 0.9896. The method exhibits good reproducibility (RSD < 3.25%) and stability (> 7 days), and quantitative detection of ONOO- was achieved in bovine serum samples. Ag nanocubes exhibited an eightfold stronger response and higher precision compared to Ag nanoparticles in ONOO- detection. This simple detection technique offers a promising method for the accurate, quantitative detection of ONOO- in wide range of biological systems.

Surface-Enhanced Raman Spectroscopy for Nitrite Detection

Nitrite is an important chemical intermediate in the nitrogen cycle and is ubiquitously present in environmental and biological systems as a metabolite or additive in the agricultural and food industries. However, nitrite can also be toxic in excessive concentrations. As such, the development of quick, sensitive, and portable assays for its measurement is desirable. In this review, we summarize the working principles and applications of surface-enhanced Raman spectroscopy (SERS) as a rapid, portable, and ultrasensitive method for nitrite detection and showcase its applicability in various water, food, and biological samples. The challenges and opportunities for future developments are also discussed.

Surface-Enhanced Raman Spectroscopy for the Detection of Reactive Oxygen Species

Reactive oxygen species (ROS) play fundamental roles in various biological and chemical processes in nature and industries, including cell signaling, disease development and aging, immune defenses, environmental remediation, pharmaceutical syntheses, metal corrosion, energy production, etc. As such, their detection is of paramount importance, but their accurate identification and quantification are technically challenging due to their transient nature with short lifetimes and low steady-state concentrations. As a highly sensitive and selective analytical technique, surface-enhanced Raman spectroscopy (SERS) is promising for detecting ROS in real-time, enabling in situ monitoring of ROS-involved electrochemical and biochemical events with exceptional resolution. This review provides a comprehensive analysis of the state-of-the-art in the SERS-based detection of ROS. Herein, the principles and ROS sensing mechanisms of SERS have been critically evaluated, highlighting their emerging applications in direct and indirect ROS monitoring in electrochemical and biological systems. The developments and reaction schemes of selective SERS probes for superoxide (•O2-), hydroxyl radicals (•OH), nitric oxide (•NO), peroxynitrite (ONOO-), and hypochlorite (OCl-) are presented. Finally, technical challenges and future research directions are discussed to guide the design of SERS for ROS analysis.

Reaction-Based SERS Probes for the Detection of Raman-Inactive Species

Surface-enhanced Raman spectroscopy (SERS) has the advantages of high sensitivity, low water interference, narrow spectral peaks for multicomponent analysis, and rich molecular fingerprint information, presenting great potential to be a robust analytical technology. However, a key issue is the unavailability in directly detecting Raman-inactive species with a small Raman scattering cross-section. Current research has addressed this issue by using specific chemical reactions to induce significant characteristic changes in SERS signals, enabling the sensitive and selective detection of Raman-inactive species. This reaction-activated SERS sensing strategy provides a clever approach to the precise determination of Raman-inactive species. In this review, we have first summarized the design principles and types of reaction-based SERS probes. Furthermore, we have examined the enormous potential of reaction-based SERS probes in the detection of bioactive species, environmental pollutants, and food contaminants. Finally, we have discussed in depth the challenges and prospects of reaction-based SERS probes on stability, reliability, and intelligence. The review is aimed to inspire a more advanced design of reaction-based SERS probes, thus further facilitating their extensive applications in SERS analysis.

Monitoring lipopolysaccharide-induced macrophage polarization by surface-enhanced Raman scattering

Macrophages are among the most important components of the innate immune system where the interaction of pathogens and their phagocytosis occur as the first barrier of immunity. When nanomaterials interact with the human body, they have to face macrophages as well. Thus, understanding of nanomaterials-macrophage interactions and underlying mechanisms is crucial. For this purpose, various methods are used. In this study, surface-enhanced Raman scattering (SERS) is proposed by studying lipopolysaccharide (LPS) induced macrophage polarization using gold nanoparticles (AuNPs) as an alternative to the current approaches. For this purpose, the murine macrophage cell line, RAW 264.7 cells, was polarized by LPS, and polarization mechanisms were characterized by nitrite release and reactive oxygen species (ROS) formation and monitored using SERS. The spectral changes were interpreted based on the molecular pathways induced by LPS. Furthermore, polarized macrophages by LPS were exposed to the toxic AuNPs doses to monitor the enhanced phagocytosis and related spectral changes. It was observed that LPS induced macrophage polarization and enhanced AuNP phagocytosis by activated macrophages elucidated clearly from SERS spectra in a label-free non-destructive manner.

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.

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.

Ratiometric fluorescent biosensor for detection and real-time imaging of nitric oxide in mitochondria of living cells

Nitric oxide (NO), a ubiquitous gaseous messenger, plays critical roles in various pathological and physiological progresses. The abnormal levels of NO in organisms are closely related to a large number of maladies. Mitochondria are the main area that produce NO in mammalian cells. Thus, detecting and real-time imaging of NO in mitochondria is of great significance for exploring the biological functions of NO. Herein, a ratiometric fluorescent biosensor (Mito-GNP-pNO520) is developed for sensitive and selective detection and real-time imaging of NO in mitochondria of living cells. The detection is achieved through the fluorescence off-on response of Mito-GNP-pNO520 toward NO. This biosensor shows excellent characteristics, such as high sensitivity toward NO with a low detection limit of 0.25 nM, exclusive selectivity to NO without interference from other substances, good biological stability and low cytotoxicity. More importantly, the biosensor is specifically located in mitochondria, enabling the detection and real-time imaging of endogenous and exogenous NO in mitochondria of living cells. Therefore, our biosensor offers a new approach for dynamic detecting and real-time imaging of NO in subcellular organelles, providing an opportunity to explore new biological effects of NO.

A dual-responsive nanozyme sensor with ultra-high sensitivity and ultra-low cross-interference towards metabolic biomarker monitoring

Accurate, sensitive and selective detection of metabolic biomarkers in biofluids are of vital significance for health self-monitoring and chronic disease prevention. Here, for the first time, a smart dual-responsive nanozyme sensor (DNS) was developed for simultaneous analysis of glucose and caffeine utilizing stimuli-responsive yolk-shell gold nanoparticles (GNPs)-embedded MIL-53 (Al) (GNPs@MIL-53) structures. After the introduction of glucose, GNPs@MIL-53 displays excellent glucose oxidase (GOx)-like activity to induce the conversion of glucose to gluconic acid and H₂O₂. H₂O₂ can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) with the generation a bright-blue color, enabling in-field visualization and surface enhanced Raman scattering (SERS) detection of glucose. Upon the addition of caffeine, 2-aminoterephthalic acid modified MIL-53 can react with the caffeine to form intermolecular hydrogen-bonded complexes, leading to strong cyan fluorescence and significant Raman enhancements. The DNS with multi-channel signal outputs can simultaneously determine glucose and caffeine at concentrations of as low as 3 × 10^-8 M and 1.2 × 10^-11 M, respectively. Importantly, the DNS-based analytical system not only enables visual discrimination and accurate assay of glucose and caffeine in biofluids, but also exhibits negligible cross-interference between glucose and caffeine determination. The combined characteristics of high selectivity, enhanced accuracy and superior quantitative performance make our platform suitable for the point-of-care monitoring of chronic-disease-related metabolic biomarkers.

Emergence of Responsive Surface-Enhanced Raman Scattering Probes for Imaging Tumor-Associated Metabolites

As a core hallmark of cancer, metabolic reprogramming alters the metabolic networks of cancer cells to meet their insatiable appetite for energy and nutrient. Tumor-associated metabolites, the products of metabolic reprogramming, are valuable in evaluating tumor occurrence and progress timely and accurately because their concentration variations usually happen earlier than the aberrances demonstrated in tissue structure and function. As an optical spectroscopic technique, surface-enhanced Raman scattering (SERS) offers advantages in imaging tumor-associated metabolites, including ultrahigh sensitivity, high specificity, multiplexing capacity, and uncompromised signal intensity. This review first highlights recent advances in the development of stimuli-responsive SERS probes. Then the mechanisms leading to the responsive SERS signal triggered by tumor metabolites are summarized. Furthermore, biomedical applications of these responsive SERS probes, such as the image-guided tumor surgery and liquid biopsy examination for tumor molecular typing, are summarized. Finally, the challenges and prospects of the responsive SERS probes for clinical translation are also discussed.

Delivery of Nitric Oxide in the Cardiovascular System: Implications for Clinical Diagnosis and Therapy

Nitric oxide (NO) is a key molecule in cardiovascular homeostasis and its abnormal delivery is highly associated with the occurrence and development of cardiovascular disease (CVD). The assessment and manipulation of NO delivery is crucial to the diagnosis and therapy of CVD, such as endothelial dysfunction, atherosclerotic progression, pulmonary hypertension, and cardiovascular manifestations of coronavirus (COVID-19). However, due to the low concentration and fast reaction characteristics of NO in the cardiovascular system, clinical applications centered on NO delivery are challenging. In this tutorial review, we first summarized the methods to estimate the in vivo NO delivery process, based on computational modeling and flow-mediated dilation, to assess endothelial function and vulnerability of atherosclerotic plaque. Then, emerging bioimaging technologies that have the potential to experimentally measure arterial NO concentration were discussed, including Raman spectroscopy and electrochemical sensors. In addition to diagnostic methods, therapies aimed at controlling NO delivery to regulate CVD were reviewed, including the NO release platform to treat endothelial dysfunction and atherosclerosis and inhaled NO therapy to treat pulmonary hypertension and COVID-19. Two potential methods to improve the effectiveness of existing NO therapy were also discussed, including the combination of NO release platform and computational modeling, and stem cell therapy, which currently remains at the laboratory stage but has clinical potential for the treatment of CVD.

Gold nanoparticle integrated artificial nanochannels for label-free detection of peroxynitrite

A label-free method for rapid and highly sensitive detection of peroxynitrite (ONOO^-) was proposed by employing well-designed N-(4-aminobutyl)-N-ethylisoluminol (ABEI) capped AuNP integrated artificial nanochannels. This work paves a new pathway to develop a versatile platform for the detection of different biological small molecules and reactive species.

"Loading-type" Plasmonic Nanoparticles for Detection of Peroxynitrite in Living Cells

To date, plasmon resonance energy transfer (PRET)-based analytical approaches still inevitably suffer from limitations, such as lack of appropriate acceptor-donor pairs and the extra requirements of active groups of acceptors, which place great obstacles in extending the application of such methods, especially in the area of living cell studies. Herein, we design and fabricate a kind of "loading-type" plasmonic nanomaterials constituting gold nanoparticles as donors of PRET coated with mesoporous silicon, in which organic small molecules (CHCN) as acceptors of PRET were loaded (Au@MSN-CHCN). This "loading-type" strategy could conveniently integrate acceptor-donor pairs into one nanoparticle, so as to achieve the goal of sensitive detection of biomolecules in a complex physiological microenvironment. Based on the change of PRET efficiency of Au@MSN-CHCN induced by the specific reaction between CHCN and peroxynitrite (ONOO^-), ONOO^-, which plays an irreplaceable role in a series of physiological and pathological processes, is sensitively and selectively detected. Furthermore, in situ imaging of exogenous and endogenous ONOO^- in living cells was achieved even at a single nanoparticle level. This work provides a general approach to construct PRET probes for visualizing various biomolecules in living cells.

From single cells to complex tissues in applications of surface-enhanced Raman scattering

This tutorial review explores how three of the most common methods for introducing nanoparticles to single cells for surface-enhanced Raman scattering measurements can be adapted for experiments with complex tissues.