Polydiacetylene-based ultrastrong bioorthogonal Raman probes for targeted live-cell Raman imaging

Single Particle Semi-Reversible Solvatochromic Sensor

A semi-reversible solvatochromic sensor is presented using polydiacetylene@polydimethylsiloxane (PDA@PDMS) core-shell particles fabricated via a co-flow microfluidic method. Exposing these particles to specific volumes and types of solvents triggers the migration of unpolymerized 10,12-pentacosadiynoic acid (PCDA) monomers from the PDA core to the PDMS shell, enabling distinctive semi-reversible color-change patterns in both regions during repeated cycles of UV exposure and solvatochromism. The solvent-induced response of PDA@PDMS varies according to solvent permeability and solvent-mediated PCDA transport efficiency, which are influenced by PDMS swelling, solvent boiling point, and PCDA solubility. Compared to bare PDA particles and PDA/PDMS composite particles, PDA@PDMS exhibits superior solvent differentiation through distinct solvatochromic responses across a range of solvents. These PDA@PDMS core-shell particles offer a robust platform for real-time, precise multi-solvent detection, with significant potential for analytical and environmental monitoring applications.

A Novel SERS Silent-Region Signal Amplification Strategy for Ultrasensitive Detection of Cu2

Due to its unique molecular fingerprinting capability and multiplex detection advantages, surface-enhanced Raman scattering (SERS) has shown great application potential in the field of biological analysis. However, the weak signal intensity and large background interference significantly limited the application of SERS in biosensing and bioimaging. Loading a large amount of Raman molecules with signal in the silent region on the hotspots of the electromagnetic field of the SERS substrate can effectively avoid severe background noise signals and significantly improve the signal intensity, making the sensitivity and specificity of SERS detection remarkably improved. To achieve this goal, a new SERS signal-amplification strategy is herein reported for background-free detection of Cu2+ by using Raman-silent probes loaded on cabbage-like gold microparticles (AuMPs) with high enhancement capabilities and single-particle detection feasibility. In this work, carboxyl-modified AuMPs were used to enable Cu2+ adsorption via electrostatic interactions, followed by ferricyanide coordination with Cu2+ to introduce cyano groups, therefore generating a stable SERS signal with nearly zero background signals owing to the Raman-silent fingerprint of cyano at 2137 cm-1. Based on the signal intensity of cyano groups correlated with Cu2+ concentration resulting from the specific coordination between Cu2+ and cyanide, a novel SERS method for Cu2+ detection with high sensitivity and selectivity is proposed. It is noted that benefiting from per ferricyanide possessing six cyano groups, the established method with the advantage of signal amplification can significantly enhance the sensing sensitivity beyond conventional approaches. Experimental results demonstrated this SERS sensor possesses significant merits towards the determination of Cu2+ in terms of high selectivity, broad linear range from 1 nM to 1 mM, and low limit of detection (0.1 nM) superior to other reported colorimetric, fluorescence, and electrochemical methods. Moreover, algorithm data processing for optimization of SERS original data was further used to improve the SERS signal reliability. As the proof-of-concept demonstrations, this work paves the way for improving SERS sensing capability through the silent-range fingerprint and signal amplification strategy, and reveals SERS as an effective tool for trace detection in complex biological and environmental matrices.

Control Over Topochemical Photopolymerization and Photoisomerization in Azobenzene Tethered Chiral Diacetylenes Toward Tunable Molecular Packing and Conductivity

Polydiacetylenes (PDAs) play a pivotal role in sensing and recognition owing to their stimuli-responsive optoelectronic properties. Inducing chirality in polydiacetylenes provides an additional handle for generating tunable chiroptical behavior in materials toward chiral optoelectronics and photonics. A photopolymerizable diacetylene (DA) tethered with chiral (R/S) phenylalanine and an azobenzene photoswitch  (1R/S -DA) is designed, with a suitable control molecule 2DA devoid of the chiral motif. The designed molecules self-assemble in aqueous and organic solvent systems. The chiral PDAs show better packing efficiency in monolayers and record higher photoisomerization percentages as compared to the achiral analog. Further, higher photoisomerization percentages are observed in the organic solvent system. In both chiral (1S- PDA) and achiral (2PDA) polymers, E-Z photoisomerization leads to the weakening of the self-assembly. Microscopic and X-ray scattering investigation suggest excellent birefringence in E-1°S- PDA owing to better molecular ordering in comparison to Z-1°S- PDA and E-1a S- PDA. Better molecular ordering of the conjugated polymer in organic solvent (E-1°S- PDA) renders a higher charge storage propensity as compared to the aqueous solvent. Finally, photo-controlled E-Z isomerization in the azobenzene motifs embedded within polymer domains exhibits modulation in conductivity with E-1°S- PDA having ≈3-fold superior conductivity than Z-1°S- PDA in solution-processed thin films.

Illuminating life processes by vibrational probes

Vibration of chemical bonds can serve as imaging contrast. Vibrational probes, synergized with major advances in chemical bond imaging instruments, have recently flourished and proven valuable in illuminating life processes. Here, we review how the development of vibrational probes with optimal biocompatibility, enhanced sensitivity, multichromatic colors and diverse functionality has extended chemical bond imaging beyond the prevalent label-free paradigm into various novel applications such as imaging metabolites, metabolic imaging, drug imaging, super-multiplex imaging, vibrational profiling and vibrational sensing. These advancements in vibrational probes have greatly facilitated understanding living systems, a new field of vibrational chemical biology.

Manipulating Aromaticity to Redirect Topochemical Polymerization Pathways

Topochemical polymerization (TCP) represents an essential route to create regio- and stereoregular polymers through solid-state transformations. Herein, we present an innovative strategy for controlling topochemical polymerization pathways by tailoring the terminal group aromaticity in the para-azaquinodimethane (AQM) ring system. Substituting phenyl groups with less aromatic furyl units extends significant spin density delocalization across the conjugated core upon thermal activation, inducing significant diradicaloid characters at furyl positions and enabling unconventional reactivities in both solution and solid states. Thermal treatment in toluene yields a unique cyclophane dimer formed via furyl-methine C-C coupling, confirmed by X-ray crystallography, while solid-state reactions produce polymers formed via both intercolumnar furyl-methine coupling and intracolumnar methine-methine coupling. The spin-center-directed mechanism underlying these transformations is validated through theoretical modeling and isotopic labeling experiments. This study highlights the prowess of aromaticity modulation in functional pro-aromatic systems, which enables the synthesis of polymers with main chain structures that are otherwise difficult to access.

Photon-counting Raman spectroscopy at a MHz spectral rate for biochemical imaging of an entire organism

Raman spectroscopy, which probes fine molecular vibrations, is crucial for interpreting covalent bonds, chemical compositions, and other molecular dynamics in mixtures via their vibrational fingerprint signatures. However, over the past few decades, longstanding barriers have been encountered in both the sensitivity and speed of Raman spectroscopy, limiting its ability to be extended to broader biochemical applications. Here, we introduce a versatile analytical workhorse, the fiber-array Raman engine (termed FIRE). In FIRE, a distinctive fiber array bundle delays the Raman shifts at a scale of 3-960 ns, and a highly dynamic single-channel photon-counting detector achieves spectral measurements that outperform the best commercial confocal Raman microscope. Crucially, FIRE features a major advantage of nonrepetitive single-shot spectra measurement at a MHz repetition rate with a full Raman span (-300-4300 cm-1) covering the fingerprint, silent, C-H, and O-H regions and therefore represents a major step toward overall improving of sensitivity, speed, and spectral span. We demonstrate full Raman spectral imaging of the metabolic activity of intact Caenorhabditis elegans. FIRE exhibits superior performance to a Raman microscope in all aspects, including autofluorescence suppression, and will elucidate a variety of biochemical applications.

Targeted Raman Visualization and Mitigation of α-Synuclein Amyloidogenesis in Living Zebrafish by a Nanobody-Decorated Polydiacetylene

α-Synuclein (α-Syn) amyloidogenesis is considered a promising diagnostic marker and therapeutic target for Parkinson's disease (PD). Simultaneously visualizing and mitigating α-Syn amyloidogenesis are essential for future PD theranostics, yet they continue to pose an insurmountable challenge. This study have herein developed a nanobody-decorated polydiacetylene to approach a straightforward solution. Grafting α-Syn61-95 segment into the third complementary determining region of a parent nanobody generates an engineered nanobody X30 that can bind with α-Syn and prevent its amyloidogenesis through homotypic interaction. It next use X30 to decorate poly(deca-4,6-diynedioic acid) (PDDA), a polydiacetylene with an ultrastrong alkyne Raman signal (2120 cm-1) in the cellular silent region, to create an α-Syn targeting Raman probe PX30. The binding affinity between X30 and α-Syn can be further boosted for over 150 times attributed to the rigidity of PDDA backbone and the multivalent effect. Therefore, PX30 not only enables real-time Raman visualization of α-Syn amyloidogenesis with a high signal-to-noise ratio in living zebrafish, but also alleviates amyloidogenesis-mediated damage to zebrafish embryos by effectively inhibiting α-Syn amyloidogenesis at low stoichiometric concentrations and scavenging pathologic reactive oxygen species.

Raman spectroscopy for cell analysis: Retrospect and prospect

Cell analysis is crucial to contemporary biomedical research, as it plays a pivotal role in elucidating life processes and advancing disease diagnosis and treatment. Raman spectroscopy, harnessing distinctive molecular vibrational data, provides a non-destructive method for cell analysis. This review surveys the progress of Raman spectroscopy in cellular analysis, emphasizing its utility in identifying individual cells, monitoring biomolecules, and assessing intracellular environments. A significant focus is placed on the novel application of triple-bond molecules as Raman tags, which enhance imaging capabilities by creating a distinctive signature with minimal background noise. The summary of Raman spectroscopy studies provides a forward-looking perspective on its applications.

A fluorescence and SERS dual-mode biosensor for quantification and imaging of Mucin1 in living cells

Mucin1 (MUC1) is a cell surface transmembrane protein overexpressed in multiple types of tumor cells, which is generally considered as a tumor-associated biomarker. Thus, quantifying and imaging of MUC1 in tumor cells is of great significance for the diagnosis and biological therapy of tumors. Herein, a fluorescence (FL) and surface-enhanced Raman scattering (SERS) dual-mode biosensor was developed for sensitive detection and imaging of MUC1 in living cells. The FL-SERS biosensor was based on self-assembled satellite structures mediated by the competition of MUC1 and complementary DNA modified on Au nanostars (AuNS-cDNA-PEG) with aptamer modified on quantum dots (QD-PDDA-Apt). This biosensor achieved dual-mode quantification and imaging of MUC1 by quenching the FL signal of QD and significantly enhancing the SERS signal of PDDA through the metal FL quenching effect and hotspot effect of AuNS, respectively. The dual-mode biosensor exhibited high sensitivity to MUC1, with a detection limit of 1.19 fg/mL under FL mode and 1.16 fg/mL under SERS mode. Moreover, this biosensor displayed good selectivity, nice biological stability and low cytotoxicity. Importantly, this biosensor possessed an excellent MUC1 dual-mode imaging capability with high specificity in different tumor cells, providing a new idea for clinical diagnosis of tumors.

Tumor Receptor-Mediated Morphological Transformation and In Situ Polymerization of Diacetylene-Containing Lipidated Peptide Amphiphile on Cell Membranes for Tumor Suppression

In situ polymerization on cell membranes can decrease cell mobility, which may inhibit tumor growth and invasion. However, the initiation of radical polymerization traditionally requires exogenous catalysts or free radical initiators, which might cause side effects in normal tissues. Herein, we synthesized a Y-type diacetylene-containing lipidated peptide amphiphile (TCDA-KFFFFK(GRGDS)-YIGSR, Y-DLPA) targeting integrins and laminin receptors on murine mammary carcinoma 4T1 cells, which underwent nanoparticle-to-nanofiber morphological transformation and in situ polymerization on cell membranes. Specifically, the polymerized Y-DLPA induced 4T1 cell apoptosis and disturbed the substance exchange and metabolism. In vitro assays demonstrated that the polymerized Y-DLPA nanofibers decreased the migration capacity of 4T1 cells, potentially suppressing tumor invasion and metastasis. When administered locally to 4T1 tumor-bearing mice, the Y-DLPA nanoparticles formed a biomimetic extracellular matrix that effectively suppressed tumor growth. This study provides an in situ polymerization strategy that can serve as an effective drug-free biomaterial with low side effects for antitumor therapy.

Raman Spectral Feature Enhancement Framework for Complex Multiclassification Tasks

Raman spectroscopy enables label-free clinical diagnosis in a single step. However, identifying an individual carrying a specific disease from people with a multi-disease background is challenging. To address this, we developed a Raman spectral implicit feature augmentation with a Raman Intersection, Union, and Subtraction augmentation strategy (RIUS). RIUS expands the data set without requiring additional labeled data by leveraging set operations at the feature level, significantly enhancing model performance across various applications. On a challenging 30-class bacterial classification task, RIUS demonstrated a substantial improvement, increasing the accuracy of ResNet by 2.1% and that of SE-ResNet by 1.4%, achieving accuracies of 85.7% and 87.1%, respectively, on the Bacteria-ID-4 Data set, where RIUS improved ResNet and SE-ResNet accuracies by 13.6% and 14.5%, respectively, with only ten samples per category. When the sample size was reduced, accuracy gains increased to 31.7% and 38.3%, demonstrating the method's robustness across different sample volumes. Compared to basic augmentation, our method exhibited superior performance across various sample volumes and demonstrated exceptional adaptability to different levels of complexity. RIUS exhibited superior performance, particularly in complex settings. Moreover, cluster analysis validated the effectiveness of the implicit feature augmentation module and the consistency between theoretical design and experimental results. We further validated our approach using clinical serum samples from 70 breast cancer patients and 70 controls, achieving an AUC of 0.94 and a sensitivity of 92.9%. Our approach enhances the potential for precisely identifying diseases in complex settings and offers plug-and-play enhancement for existing classification models.

Advances in subpopulation separation and detection of extracellular vesicles: for liquid biopsy and downstream research

Extracellular vesicles (EVs) are carriers of a diverse array of bioactive molecules, making them valuable clinical tools for liquid biopsy in disease diagnosis and prognosis evaluation. These molecules play critical roles in various physiological and pathological conditions, and effective separation of EVs is essential to achieve these objectives. Due to the high heterogeneity of EVs, particularly with regard to their cargo molecules, merely isolating the general EV population is inadequate for liquid biopsy and biological function studies. Therefore, separating EV subpopulations becomes crucial. Traditional separation methods, such as differential ultracentrifugation and size exclusion chromatography, along with burgeoning techniques like classical microfluidic chips and covalent chemistry, often prove time-consuming, yield low purity, and have limited ability to address cargo heterogeneity. Thus, precise separation of EV subpopulations is of utmost importance. Additionally, detecting subpopulation-specific cargo is vital for validating the effectiveness of separation methods and supporting clinical biopsy applications. However, reviews that focus specifically on detection methods for EV subpopulations are limited. This paper provides a comprehensive overview of the methods for separating and detecting EV subpopulations with surface marker heterogeneity, comparing the advantages and limitations of each technique. Furthermore, it discusses challenges and future prospects for these methods in the context of liquid biopsy and downstream research. Collectively, this review aims to offer innovative insights into the separation and detection of EV subpopulations, guiding researchers to avoid common pitfalls and refine their investigative approaches.

Spatially Quantitative Imaging of Enzyme Activity in a Living Cell

Enzyme activity plays a key role in cell heterogeneity. Its spatially quantitative imaging in a living cell not only directly displays but also helps people to understand cell heterogeneity. Current methods are hard to achieve due to the short intracellular retention or lack of internal reference of the imaging probes. Herein, we rationally designed a self-referenced Raman probe Val-Cit-Cys(StBu)-Pra-Gly-CBT (Yne-CBT) which takes an intracellular cathepsin B (CTSB)-initiated CBT-Cys click reaction to yield a long-retained cyclic dimer in cell. In the meantime, Raman signal changes of its two chemical bonds (C≡C and C≡N) after the reaction are used for self-referencing and quantitative Raman imaging of CTSB activity. In vitro experiments demonstrated that, with shell-isolated nanoparticle-enhanced Raman spectroscopy technique, 20 μM Yne-CBT was able to quantitatively detect CTSB activity with a limit of detection of 61.4 U L-1. Under a homemade microfluidic channel, Yne-CBT was successfully applied for spatially quantitative imaging CTSB activity in a living cell. Our strategy provides people with a facile method to directly and quantitatively display cell heterogeneity.

Rapid and accurate bacteria identification through deep-learning-based two-dimensional Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) offers a distinctive vibrational fingerprint of the molecules and has led to widespread applications in medical diagnosis, biochemistry, and virology. With the rapid development of artificial intelligence (AI) technology, AI-enabled Raman spectroscopic techniques, as a promising avenue for biosensing applications, have significantly boosted bacteria identification. By converting spectra into images, the dataset is enriched with more detailed information, allowing AI to identify bacterial isolates with enhanced precision. However, previous studies usually suffer from a trade-off between high-resolution spectrograms for high-accuracy identification and short training time for data processing. Here, we present an efficient bacteria identification strategy that combines deep learning models with a spectrogram encoding algorithm based on wavelet packet transform and Gramian angular field techniques. In contrast to the direct analysis of raw Raman spectra, our approach utilizes wavelet packet transform techniques to compress the spectra by a factor of 1/15, while concurrently maintaining state-of-the-art accuracy by amplifying the subtle differences via Gramian angular field techniques. The results demonstrate that our approach can achieve a 99.64 % and a 90.55 % identification accuracy for two types of bacterial isolates and thirty types of bacterial isolates, respectively, while a 90 % reduction in training time compared to the conventional methods. To verify the model's stability, Gaussian noises were superimposed on the testing dataset, showing a specific generalization ability and superior performance. This algorithm has the potential for integration into on-site testing protocols and is readily updatable with new bacterial isolates. This study provides profound insights and contributes to the current understanding of spectroscopy, paving the way for accurate and rapid bacteria identification in diverse applications of environment monitoring, food safety, microbiology, and public health.

Regulating Electron Acceptor Unit to Construct Conjugated Polymer Probe for Raman Imaging of Tumor and Sentinel Lymph Nodes

Donor-acceptor (D-A) conjugated polymers have large Stokes shifts, high photostability, and good biocompatibility and thus are ideal for use as Raman probes in vivo. However, few D-A conjugated polymers are used as Raman probes for Raman imaging due to their weak Raman signal intensity and intrinsic fluorescence interference. Here, we developed a D-A conjugated polymer probe (CDT-TT) containing alternating cyclopentadithiophene-thienothiophene units for Raman imaging of tumor and sentinel lymph nodes (SLNs). The CDT-TT shows a strong Raman signal at 1389 cm-1 without fluorescence and lipid background signal interference under 785 nm near-infrared light. Moreover, the CDT-TT loaded nanoparticles realized the accurate imaging of tumor cells and tumor tissues. In addition, a high-resolution margin imaging of in situ SLNs was acquired. Taken together, the established method is effective for accurate Raman detection of tumors and SLNs, which may shed new light on the development of D-A polymer Raman probes for clinical imaging.

Novel Ratiometric Surface-Enhanced Raman Scattering (SERS) Biosensor for Ultrasensitive Quantitative Monitoring of Human Carboxylesterase-1 in Hepatocellular Carcinoma Cells Using Ag-Au Nanoflowers as SERS Substrate

In this study, we developed ratiometric surface-enhanced Raman scattering (SERS) biosensors using Ag-Au alloy nanoflowers as SERS substrates, molecules having amide bonds and alkyne groups (Tag A) as Raman reporters, and sodium thiocyanate as an internal standard molecule (Tag B) for the sensitive detection of human carboxylesterase-1 (hCE1) in HepG-2 cells. The correlation between HepG-2 cell damage and hCE1 activity levels was investigated. Both Tag A's alkyne group and Tag B's cyanide group produced characteristic SERS signals in the Raman-silent region (I2000 cm-1 and I2115 cm-1, respectively). The hydrolysis of the amide bond in Tag A via hCE1 and the shedding of the alkyne group led to a reduction in the SERS signal intensity observed at I2000 cm-1. Conversely, the SERS signal intensity of Tag B at I2115 cm-1 exhibited a consistent pattern. As the activity level of hCE1 and the ratiometric peak intensity (I2000 cm-1/I2115 cm-1) correlated negatively, hCE1 could be quantitatively detected within the range of 10-2 to 2 × 102 ng·mL-1, with a detection limit of 7.3 pg·mL-1. The ratiometric SERS probe strategy, in which a ratio response is employed, permits sensitive and reproducible SERS detection by facilitating intrinsic calibration to rectify signal fluctuations resulting from temporal and spatial variations in the detection conditions. Concurrently, the implementation of Raman-silent region reporter molecules mitigates the interference from endogenous biomolecules in SERS measurements and offers a novel approach for achieving highly sensitive and interference-free detection of intracellular hCE1.

A microenvironment-modulating dressing with proliferative degradants for the healing of diabetic wounds

Diabetic wounds are usually entangled in a disorganized and self-perpetuating microenvironment and accompanied by a prolonged delay in tissue repair. Sustained and coordinated microenvironment regulation and tissue regeneration are key to the healing process of diabetic wounds, yet they continue to pose a formidable challenge. Here we report a rational double-layered dressing design based on chitosan and a degradable conjugated polymer polydiacetylene, poly(deca-4,6-diynedioic acid) (PDDA), that can meet this intricate requirement. With an alternating ene-yne backbone, PDDA degrades when reacting with various types of reactive oxygen species (ROS), and more importantly, generates proliferative succinic acid as a major degradant. Inheriting from PDDA, the developed PDDA-chitosan double layer dressing (PCD) can eliminate ROS in the microenvironment of diabetic wounds, alleviate inflammation, and downregulate gene expression of innate immune receptors. PCD degradation also triggers simultaneous release of succinic acid in a sustainable manner, enabling long-term promotion on tissue regeneration. We have validated the biocompatibility and excellent performance of PCD in expediting the wound healing on both diabetic mouse and porcine models, which underscores the significant translational potential of this microenvironment-modulating, growth-promoting wound dressing in diabetic wounds care.

Biomimetic Gold Nanorods-Manganese Porphyrins with Surface-Enhanced Raman Scattering Effect for Photoacoustic Imaging-Guided Photothermal/Photodynamic Therapy

Surface-enhanced Raman scattering (SERS) imaging integrating photothermal and photodynamic therapy (PTT/PDT) is a promising approach for achieving accurate diagnosis and effective treatment of cancers. However, most available Raman reporters show multiple signals in the fingerprint region, which overlap with background signals from cellular biomolecules. Herein, a 4T1 cell membrane-enveloped gold nanorods-manganese porphyrins system (GMCMs) is designed and successfully fabricated as a biomimetic theranostic nanoplatform. Manganese porphyrins are adsorbed on the surface of Au nanorods via the terminal alkynyl group. Cell membrane encapsulation protects the manganese porphyrins from falling off the gold nanorods. The biomimetic GMCMs confirm specific homologous targeting to 4T1 cells with good dispersibility, excellent photoacoustic (PA) imaging properties, and preferable photothermal and 1O2 generation performance. GMCMs exhibit distinct SERS signals in the silent region without endogenous biomolecule interference both in vitro and in vivo. Manganese ions could not only quench the fluorescence of porphyrins to enhance the SERS imaging effect but also deplete cellular GSH to increase 1O2 yield. Both in vitro and in vivo studies demonstrate that GMCMs effectively eradicate tumors through SERS/PA imaging-guided PTT/PDT. This study provides a feasible strategy for augmenting the Raman imaging effects of the alkynyl group and integrating GSH-depletion to enhance PTT/PDT efficacy.

Topochemical Polymerization at Diacetylene Metal-Organic Framework Thin Films for Tuning Nonlinear Optics

Developing the topochemical polymerization of metal-organic frameworks (MOFs) is of pronounced significance for expanding their functionalities but is still a challenge on third-order nonlinear optics (NLO). Here, we report diacetylene MOF (CAS-1-3) films prepared using a stepwise deposition method and film structural transformation approach, featuring dynamic structural diversity. The MOF structures were determined by the three-dimensional electron diffraction (3D ED) method from nanocrystals collected from the films, which provides a reliable strategy for determining the precise structure of unknown MOF films. We demonstrate the well-aligned diacetylene groups in the MOFs can promote topological polymerization to produce a highly conjugated system under thermal stimulation. As a result, the three MOF films have distinct NLO properties: the CAS-1 film exhibits saturable absorption (SA) while CAS-2 and CAS-3 films exhibit reverse saturable absorption (RSA). Interestingly, due to the topochemical polymerization of the MOF films, a transition from SA to RSA response was observed with increasing temperatures, and the optical limiting effect was significantly enhanced (∼46 times). This study provides a new strategy for preparing NLO materials and thermally regulation of nonlinear optics.

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.

Covalent Organic Framework-Structured Raman Probes for Ultrasensitive In Vivo Bioimaging

Organic Raman probes, including polymers and small molecules, have attracted great attention in biomedical imaging owing to their excellent biocompatibility. However, the development of organic Raman probes is usually hindered by a mismatch between their absorption spectra and wavelength-fixed excitation, which makes it difficult to achieve resonance excitation necessary to obtain strong Raman signals. Herein, we introduce a covalent organic framework (COF) into the fine absorption spectrum regulation of organic Raman probes, resulting in their significant Raman signal enhancement. In representative examples, a polymer poly(diketopyrrolopyrrole-p-phenylenediamine) (DPP-PD) and a small molecule azobenzene are transformed into the corresponding COF-structured Raman probes. Their absorption peaks show an accurate match of less than 5 nm with the NIR excitation. As such, the COF-structured Raman probes acquire highly sensitive bioimaging capabilities compared to their precursors with negligible signals. By further mechanism studies, we discover that the crystallinity and size of COFs directly affect the π-conjugation degree of Raman probes, thus changing their bandgaps and absorption spectra. Our study offers a universal and flexible method for improving the signal performance of organic Raman probes without changing their structural units, making it more convenient to obtain the highly sensitive organic Raman probes for in vivo bioimaging.

Viewing 3D spatial biology with highly-multiplexed Raman imaging: from spectroscopy to biotechnology

Understansding complex biological systems requires the simultaneous characterization of a large number of interacting components in their native 3D environment with high spatial resolution. Highly-multiplexed Raman imaging is an emerging general strategy for detecting biomarkers with scalable multiplexity and ultra-sensitivity based on a series of stimulated Raman scattering (SRS) techniques. Here we review recent advances in highly-multiplexed Raman imaging and how they contribute to the technological revolution in 3D spatial biology, focusing on the developmental pathway from spectroscopy study to biotechnology invention. We envision highly-multiplexed Raman imaging is taking off, which will greatly facilitate our understanding in biological and medical research fields.

On-Chip Capture, Raman-Silent Polymer Labeling, and Digital Mapping Analysis of Escherichia coli O157:H7 in Beverages All-in-One

Escherichia coli O157:H7 is one of the most susceptible foodborne pathogens, easily causing food poisoning and other health risks. It is of great significance to establish a quantitative method with higher sensitivity and less time consumption for foodborne pathogens analysis. The Raman-silent signal has a good performance for avoiding interference from the food matrix so as to achieve accurate signal differentiation. In this work, we presented a preparation-mapping all-in-one method for digital mapping analysis. We prepared a functionalized Raman-silent polymer label of Escherichia coli O157:H7, which was captured on a porous 4-mercaptophenylboric acid@Ag foam chip. To improve accuracy and widen the detection range, a digital mapping quantitative strategy was employed in data extraction and processing. By transfer mapping information into digitized statistical results, the limitation of obtaining reproducible intensity values just by randomly selected spots on the substrate can be addressed. With a wide linear range of 1.0 × 101-1.0 × 105 CFU mL-1 and a limit of detection of 4.4 CFU mL-1, this all-in-one method had good sensitivity performance. Also, this method achieved good precision and selectivity in a series of experiments and was successfully applied to the analysis of beverage samples.

Degradable π-Conjugated Polymers

The integration of next-generation electronics into society is rapidly reshaping our daily interactions and lifestyles, revolutionizing communication and engagement with the world. Future electronics promise stimuli-responsive features and enhanced biocompatibility, such as skin-like health monitors and sensors embedded in food packaging, transforming healthcare and reducing food waste. Imparting degradability may reduce the adverse environmental impact of next-generation electronics and lead to opportunities for environmental and health monitoring. While advancements have been made in producing degradable materials for encapsulants, substrates, and dielectrics, the availability of degradable conducting and semiconducting materials remains restricted. π-Conjugated polymers are promising candidates for the development of degradable conductors or semiconductors due to the ability to tune their stimuli-responsiveness, biocompatibility, and mechanical durability. This perspective highlights three design considerations: the selection of π-conjugated monomers, synthetic coupling strategies, and degradation of π-conjugated polymers, for generating π-conjugated materials for degradable electronics. We describe the current challenges with monomeric design and present options to circumvent these issues by highlighting biobased π-conjugated compounds with known degradation pathways and stable monomers that allow for chemically recyclable polymers. Next, we present coupling strategies that are compatible for the synthesis of degradable π-conjugated polymers, including direct arylation polymerization and enzymatic polymerization. Lastly, we discuss various modes of depolymerization and characterization techniques to enhance our comprehension of potential degradation byproducts formed during polymer cleavage. Our perspective considers these three design parameters in parallel rather than independently while having a targeted application in mind to accelerate the discovery of next-generation high-performance π-conjugated polymers for degradable organic electronics.

Seeing is Believing: Developing Multimodal Metabolic Insights at the Molecular Level

This outlook explores how two different molecular imaging approaches might be combined to gain insight into dynamic, subcellular metabolic processes. Specifically, we discuss how matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) and stimulated Raman scattering (SRS) microscopy, which have significantly pushed the boundaries of imaging metabolic and metabolomic analyses in their own right, could be combined to create comprehensive molecular images. We first briefly summarize the recent advances for each technique. We then explore how one might overcome the inherent limitations of each individual method, by envisioning orthogonal and interchangeable workflows. Additionally, we delve into the potential benefits of adopting a complementary approach that combines both MSI and SRS spectro-microscopy for informing on specific chemical structures through functional-group-specific targets. Ultimately, by integrating the strengths of both imaging modalities, researchers can achieve a more comprehensive understanding of biological and chemical systems, enabling precise metabolic investigations. This synergistic approach holds substantial promise to expand our toolkit for studying metabolites in complex environments.

A WOx/MoOx hybrid oxide based SERS FET and investigation on its tunable SERS performance

Active control of the surface-enhanced Raman scattering (SERS) enhancement shows great potential for realizing smart detection of different molecules. However, conventional methods usually involve time-consuming structural design or a sophisticated fabrication process. Herein, we reported an electrically tunable field effect transistor (FET) comprising a WOx/MoOx hybrid as the SERS active layer. In the experiment, WOx/MoOx hybrids were first prepared by mixing different molar ratios of WOx and MoOx oxides. Then, R6G molecules were used as Raman reporters, showing that the intensity of the SERS signal observed on the most optimal hybrids (molar ratio = 1 : 3) could be increased by two times as high as that observed on a single WOx or MoOx based substrate, which was ascribed to enhanced charge transfer efficiency by the constructed nano-heterojunction between the WOx and MoOx oxides. Thereafter, a back-gate FET was fabricated on a SiO2/Si substrate, and the most optimal WOx/MoOx hybrid was deposited as the gate channel and the SERS active layer. After that, a series of gate biases (from -15 V to 15 V) were implemented to actively tune the SERS performance of the FET. It is evident that the SERS EF can be further tuned from 2.39 × 107 (-15 V) to 6.55 × 107 (+10 V), which is ∼7.4/4.1 times higher than that observed on the pure WOx device (8.81 × 106) or pure MoOx (1.61 × 107) device, respectively. Finally, the mechanism behind the electrical tuning strategy was investigated. It is revealed that a positive voltage would bend the conduction band down, which increased the electron density near the Fermi level. Consequently, it triggered the resonance charge transfer and significantly improved the SERS performance. In contrast, a negative gate voltage attracted the holes to the Fermi level, which deferred the charge transfer process, and caused the reduction of the SERS enhancement.

Carbon-Iodine Polydiacetylene Nanofibers for Image-Guided Radiotherapy and Tumor-Microenvironment-Enhanced Radiosensitization

Radiotherapy is a mainstay treatment used in clinics for locoregional therapy, although it still represents a great challenge to improve the sensitivity and accuracy of radiotherapy for tumors. Here, we report the conjugated polymer, polydiiododiacetylene (PIDA), with an iodine content of 84 wt %, as a highly effective computed tomography (CT) contrast agent and tumor microenvironment-responsive radiosensitizer. PIDA exhibited several key properties that contribute to the improvement of precision radiotherapy. The integrated PIDA nanofibers confined within the tumor envelope demonstrated amplified CT intensity and prolonged retention, providing an accurate calculation of dose distribution and precise radiation delivery for CT image-guided radiotherapy. Therefore, our strategy pioneers PIDA nanofibers as a bridge to cleverly connect a fiducial marker to guide accurate radiotherapy and a radiosensitizer to improve tumor sensitivity, thereby minimizing potential damage to surrounding tissues and facilitating on-demand therapeutic intervention in tumors.

Photochemically and Thermally Programmed Optical Multi-States from a Single Diacetylene-Functionalized Cyanostilbene Luminogen

To develop advanced optical systems, many scientists have endeavored to create smart optical materials which can tune their photophysical properties by changing molecular states. However, optical multi-states are obtained usually by mixing many dyes or stacking multi-layered structures. Here, multiple molecular states are tried to be generated with a single dye. In order to achieve the goal, a diacetylene-functionalized cyanostilbene luminogen (DACSM) is newly synthesized by covalently connecting diacetylene and cyanostilbene molecular functions. Photochemical reaction of cyanostilbene and topochemical polymerization of diacetylene can change the molecular state of DACSM. By thermal stimulations and the photochemical reaction, the conformation of polymerized DACSM is further tuned. The synergetic molecular cooperation of cyanostilbene and diacetylene generates multiple molecular states of DACSM. Utilizing the optical multi-states achieved from the newly developed DACSM, switchable optical patterns and smart secret codes are successfully demonstrated.

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.

Development of a universal method for vibrational analysis of the terminal alkyne C≡C stretch

The terminal alkyne C≡C stretch has a large Raman scattering cross section in the "silent" region for biomolecules. This has led to many Raman tag and probe studies using this moiety to study biomolecular systems. A computational investigation of these systems is vital to aid in the interpretation of these results. In this work, we develop a method for computing terminal alkyne vibrational frequencies and isotropic transition polarizabilities that can easily and accurately be applied to any terminal alkyne molecule. We apply the discrete variable representation method to a localized version of the C≡C stretch normal mode. The errors of (1) vibrational localization to the terminal alkyne moiety, (2) anharmonic normal mode isolation, and (3) discretization of the Born-Oppenheimer potential energy surface are quantified and found to be generally small and cancel each other. This results in a method with low error compared to other anharmonic vibrational methods like second-order vibrational perturbation theory and to experiments. Several density functionals are tested using the method, and TPSS-D3, an inexpensive nonempirical density functional with dispersion corrections, is found to perform surprisingly well. Diffuse basis functions are found to be important for the accuracy of computed frequencies. Finally, the computation of vibrational properties like isotropic transition polarizabilities and the universality of the localized normal mode for terminal alkynes are demonstrated.

Triple-Bond Vibrations: Emerging Applications in Energy and Biological Sciences

Triple bonds, such as that formed between two carbon atoms (i.e., C≡C) or that formed between one carbon atom and one nitrogen atom (i.e., C≡N), afford unique chemical bonding and hence vibrational characteristics. As such, they are not only frequently used to construct molecules with tailored chemical and/or physical properties but also employed as vibrational probes to provide site-specific chemical and/or physical information at the molecular level. Herein, we offer our perspective on the emerging applications of various triple-bond vibrations in energy and biological sciences with a focus on C≡C and C≡N triple bonds.

Conjugation Length-Dependent Raman Scattering Intensity of Conjugated Polymers

Polydiacetylenes, as a class of conjugated polymers with alternating conjugated C═C and C≡C bonds, have emerged as a promising probe material for biomedical Raman imaging, given their ultrastrong Raman scattering intensity. However, the relationship between the structure, especially the molecular length of polydiacetylenes, and their Raman scattering intensity remains unclear. In this work, a series of water-soluble polydiacetylenes, namely poly(deca-4,6-diynedioic acid) (PDDA) with different molecular weights (MWs), is prepared through controlled polymerization and degradation. The ultraviolet-visible (UV-vis) absorption spectroscopic and Raman spectroscopic studies on these polymers reveal that the Raman scattering intensity of PDDA increases nonlinearly with the MW. The MW-Raman scattering intensity relationship in the polymerization process is completely different from that in the degradation process. In contrast, the Raman scattering intensity increases more linearly with the maximal absorbance of the polymer, and the relationship between the Raman scattering intensity and the maximal absorbance of PDDA in the polymerization process is consistent with that in the degradation process. The Raman scattering intensity of PDDA hence exhibits a better dependence on the effective conjugation length of the polymer, which should guide the future design of conjugated polymers for Raman imaging applications.

Strategies and Progress of Raman Technologies for Cellular Uptake Analysis of the Drug Delivery Systems

Nanoparticle (NP)-based drug delivery systems have the potential to significantly enhance the pharmacological and therapeutic properties of drugs. These systems enhance the bioavailability and biocompatibility of pharmaceutical agents via enabling targeted delivery to specific tissues or organs. However, the efficacy and safety of these systems are largely dependent on the cellular uptake and intracellular transport of NPs. Thus, it is crucial to monitor the intracellular behavior of NPs within a single cell. Yet, it is challenging due to the complexity and size of the cell. Recently, the development of the Raman instrumentation offers a versatile tool to allow noninvasive cellular measurements. The primary objective of this review is to highlight the most recent advancements in Raman techniques (spontaneous Raman scattering, bioorthogonal Raman scattering, coherence Raman scattering, and surface-enhanced Raman scattering) when it comes to assessing the internalization of NP-based drug delivery systems and their subsequent movement within cells.

Boosting the Brightness of Raman Tags Using Cyanostar Macrocycles

Raman probes have received growing attention for their potential use in super-multiplex biological imaging and flow cytometry applications that cannot be achieved using fluorescent probes. However, obtaining strong Raman scattering signals from small Raman probes has posed a challenge that holds back their practical implementation. Here, we present new types of Raman-active nanoparticles (Rdots) that incorporate ionophore macrocycles, known as cyanostars, to act as ion-driven and structure-directing spacers to address this problem. These macrocycle-enhanced Rdots (MERdots) exhibit sharper and higher electronic absorption peaks than Rdots. When combined with resonant broadband time-domain Raman spectroscopy, these MERdots show a ∼3-fold increase in Raman intensity compared to conventional Rdots under the same particle concentration. Additionally, the detection limit on the concentration of MERdots is improved by a factor of 2.5 compared to that of Rdots and a factor of 430 compared to that of Raman dye molecules in solution. The compact size of MERdots (26 nm in diameter) and their increased Raman signal intensity, along with the broadband capabilities of time-domain resonant Raman spectroscopy, make them promising candidates for a wide range of biological applications.

Ultrasound-Triggered Cascade Amplification of Nanotherapy

Ultrasound (US)-triggered cascade amplification of nanotherapies has attracted considerable attention as an effective strategy for cancer treatment. With the remarkable advances in materials chemistry and nanotechnology, a large number of well-designed nanosystems have emerged that incorporate presupposed cascade amplification processes and can be activated to trigger therapies such as chemotherapy, immunotherapy, and ferroptosis, under exogenous US stimulation or specific substances generated by US actuation, to maximize antitumor efficacy and minimize detrimental effects. Therefore, summarizing the corresponding nanotherapies and applications based on US-triggered cascade amplification is essential. This review comprehensively summarizes and highlights the recent advances in the design of intelligent modalities, consisting of unique components, distinctive properties, and specific cascade processes. These ingenious strategies confer unparalleled potential to nanotherapies based on ultrasound-triggered cascade amplification and provide superior controllability, thus overcoming the unmet requirements of precision medicine and personalized treatment. Finally, the challenges and prospects of this emerging strategy are discussed and it is expected to encourage more innovative ideas and promote their further development.

Revealing Population Heterogeneity in Vesicle-Based Nanomedicines Using Automated, Single Particle Raman Analysis

The intrinsic heterogeneity of many nanoformulations is currently challenging to characterize on both the single particle and population level. Therefore, there is great opportunity to develop advanced techniques to describe and understand nanomedicine heterogeneity, which will aid translation to the clinic by informing manufacturing quality control, characterization for regulatory bodies, and connecting nanoformulation properties to clinical outcomes to enable rational design. Here, we present an analytical technique to provide such information, while measuring the nanocarrier and cargo simultaneously with label-free, nondestructive single particle automated Raman trapping analysis (SPARTA). We first synthesized a library of model compounds covering a range of hydrophilicities and providing distinct Raman signals. These compounds were then loaded into model nanovesicles (polymersomes) that can load both hydrophobic and hydrophilic cargo into the membrane or core regions, respectively. Using our analytical framework, we characterized the heterogeneity of the population by correlating the signal per particle from the membrane and cargo. We found that core and membrane loading can be distinguished, and we detected subpopulations of highly loaded particles in certain cases. We then confirmed the suitability of our technique in liposomes, another nanovesicle class, including the commercial formulation Doxil. Our label-free analytical technique precisely determines cargo location alongside loading and release heterogeneity in nanomedicines, which could be instrumental for future quality control, regulatory body protocols, and development of structure-function relationships to bring more nanomedicines to the clinic.

Multivalent Nanobody Conjugate with Rigid, Reactive Oxygen Species Scavenging Scaffold for Multi-Target Therapy of Alzheimer's Disease

Efficient therapeutic strategies that concurrently target both Aβ aggregation and oxidative stress in the Alzheimer's disease (AD) microenvironment emerge as a cutting-edge tool to combat the intricate pathogenesis of AD. Here, a multivalent nanobody conjugate with rigid, reactive oxygen species (ROS) scavenging scaffold is developed to achieve simultaneous Aβ amyloidogenesis mitigation, ROS elimination, and Aβ plaque clearance. Grafting Aβ segment (33-GLMVGGVVIA-42) into the third complementary-determining region of a parent nanobody generates an engineered nanobody NB that can recognize Aβ and inhibit its aggregation through homotypic interactions. NB is further genetically modified with a fragment of human interleukin-1β (163-VQGEESNDK-171), so that the obtained fusion nanobody NBIL can also facilitate the Aβ clearance by microglia. Linking NBIL covalently onto a rigid, ROS scavenging scaffold poly(deca-4,6-diynedioic acid) (PDDA) creates the multivalent nanobody conjugate PNBIL, which not only boosts the binding affinity between NBIL and Aβ aggregates for nearly 100 times but also possesses a long-term capability of oxidative stress alleviation, inflammation reduction, and neuron protection. PNBIL has significantly attenuated symptoms on two AD mouse models through amyloidogenesis inhibition and AD microenvironment modulation, validating that the multivalent nanobody conjugate design based on combinatory nanobody and molecular engineering is a promising approach of multi-target therapeutic strategies.

Bioorthogonal surface-enhanced Raman scattering flower-like nanoprobe with embedded standards for accurate cancer cell imaging

Developing precise and effective strategies for cancer identification and imaging is attractive due to their importance for early cancer detection, prognosis, and subsequent treatment. Herein, we reported a novel bioorthogonal surface-enhanced Raman scattering (SERS) nanoprobe for accurate cancer cell imaging. A novel core-molecule-shell nanoflower (Au@4-MBN@Au) with rich electromagnetic hot spots and enhanced Raman scattering was first synthesized by optimizing the embedded concentrations of 4-mercaptobenzonitrile (4-MBN). Then, Au@4-MBN@Au was further modified with FA-PEG-SH molecules to acquire the bioorthogonal SERS nanoprobe Au@4-MBN@Au-PEG-FA. The SERS nanoprobe illustrated a robust and stable nitrile stretching vibration Raman signal (2223 cm^-1) in the cellular silent region, ensuring high sensitivity and ultra-accuracy SERS imaging of cancer cells. Furthermore, cell imaging results demonstrated Au@4-MBN@Au-PEG-FA could recognize FR-positive HeLa cells with high selectivity due to the high affinity between folate receptor and folic acid. More notably, Au@4-MBN@Au-PEG-FA has been applied to identify FR-positive Hela cells from co-cultured cancer cells with similar morphology by SERS imaging for the first time. With improved signal-to-background ratio, high selectivity, and excellent stability, we anticipate the SERS nanoprobe Au@4-MBN@Au-PEG-FA could be applied for FR-related cancer theranostics and clinical detection in the future.

Resonant Raman-Active Polymer Dot Barcodes for Multiplex Cell Mapping

Resonance Raman spectroscopy is an efficient tool for multiplex imaging because of the narrow bandwidth of the electronically enhanced vibrational signals. However, Raman signals are often overwhelmed by concurrent fluorescence. In this study, we synthesized a series of truxene-based conjugated Raman probes to show structure-specific Raman fingerprint patterns with a common 532 nm light source. The subsequent polymer dot (Pdot) formation of the Raman probes efficiently suppressed fluorescence via aggregation-induced quenching and improved the dispersion stability of particles without leakage of Raman probes or particle agglomeration for more than 1 year. Additionally, the Raman signal amplified by electronic resonance and increased probe concentration exhibited over 10³ times higher relative Raman intensities versus 5-ethynyl-2'-deoxyuridine, enabling successful Raman imaging. Finally, multiplex Raman mapping was demonstrated with a single 532 nm laser using six Raman-active and biocompatible Pdots as barcodes for live cells. Resonant Raman-active Pdots may suggest a simple, robust, and efficient way for multiplex Raman imaging using a standard Raman spectrometer, suggesting the broad applicability of our strategy.

Design and Synthesis of SERS Materials for In Vivo Molecular Imaging and Biosensing

Surface-enhanced Raman scattering (SERS) is a feasible and ultra-sensitive method for biomedical imaging and disease diagnosis. SERS is widely applied to in vivo imaging due to the development of functional nanoparticles encoded by Raman active molecules (SERS nanoprobes) and improvements in instruments. Herein, the recent developments in SERS active materials and their in vivo imaging and biosensing applications are overviewed. Various SERS substrates that have been successfully used for in vivo imaging are described. Then, the applications of SERS imaging in cancer detection and in vivo intraoperative guidance are summarized. The role of highly sensitive SERS biosensors in guiding the detection and prevention of diseases is discussed in detail. Moreover, its role in the identification and resection of microtumors and as a diagnostic and therapeutic platform is also reviewed. Finally, the progress and challenges associated with SERS active materials, equipment, and clinical translation are described. The present evidence suggests that SERS could be applied in clinical practice in the future.

Spatiotemporal Ultrasound-Driven Bioorthogonal Catalytic Therapy

Bioorthogonal chemistry, referring to the rapid and selective synthesis of imaging and/or therapeutic molecules in live animals via transition metal-mediated non-natural chemical transformation without disrupting endogenous reactions, has greatly expanded the tools and techniques for biomedicine. However, owing to safety concerns associated with metal toxicity, selectivity, sensitivity and stability, efficient bioorthogonal reactions that can be reliably executed in complex biological environments remain challenging. In this study, an intelligent, versatile bioorthogonal catalyst based on ultrasmall poly(acrylic acid)-modified copper nanocomplexes (Cu@PAA NCs) to achieve high spatiotemporal catalytic efficacy is established. The catalytic activity of the Cu@PAA NCs can be reversibly regulated via valence state interconversion between Cu(II) and Cu(I) under exogenous ultrasound irradiation, promoting off-target prodrug activation in lesion sites through the Cu(I)-catalyzed azide-alkyne cycloaddition reaction. Moreover, ultrasound-triggered electron-hole separation endows the Cu@PAA NCs with robust sonosensitizing ability for sonodynamic therapy. Furthermore, the Cu@PAA NCs exhibit enhanced contrast in magnetic resonance and photoacoustic imaging. Notably, the renal-clearable Cu@PAA NCs exhibit intrinsically benign biocompatibility. This spatiotemporally ultrasound-mediated bioorthogonal catalysis not only expands the repertoire of in situ therapeutic agents but also provides a new avenue for disease theranostics.

A Background-Free SERS Strategy for Sensitive Detection of Hydrogen Peroxide

The accurate and sensitive detection of biomolecules by surface-enhanced Raman spectroscopy (SERS) is possible, but remains challenging due to the interference from biomolecules in complex samples. Herein, a new SERS sensor is developed for background-free detection of hydrogen peroxide (H₂O₂) with an ultralow detection limit (1 × 10^-10 mol/L), using a Raman-silent strategy. The Au microparticles (Au-RSMPs) resembling rose-stones are devised as SERS substrates with a high enhancement effect, and 4-mercaptophenylboronic acid (4-MPBA) is selected as an H₂O₂-responsive Raman reporter. Upon the reaction with H₂O₂, the phenylboronic group of 4-MPBA was converted to a phenol group, which subsequently reacted with 4-diazonium-phenylalkyne (4-DP), an alkyne-carrying molecule via the azo reaction. The formed product exhibits an intense and sharp SERS signal in the Raman-silent region, avoiding interference of impurities and biomolecules. As a proof-of-concept demonstration, we show that this SERS sensor possesses significant merits towards the determination of H₂O₂ in terms of broad linear range, low limit of detection, and high selectivity, showing promise for the quantitative analysis of H₂O₂ in complicated biological samples.

Near infrared-activatable biomimetic nanogels enabling deep tumor drug penetration inhibit orthotopic glioblastoma

Glioblastoma multiforme (GBM) is one of the most fatal malignancies due to the existence of blood-brain barrier (BBB) and the difficulty to maintain an effective drug accumulation in deep GBM lesions. Here we present a biomimetic nanogel system that can be precisely activated by near infrared (NIR) irradiation to achieve BBB crossing and deep tumor penetration of drugs. Synthesized by crosslinking pullulan and poly(deca-4,6-diynedioic acid) (PDDA) and loaded with temozolomide and indocyanine green (ICG), the nanogels are inert to endogenous oxidative conditions but can be selectively disintegrated by ICG-generated reactive oxygen species upon NIR irradiation. Camouflaging the nanogels with apolipoprotein E peptide-decorated erythrocyte membrane further allows prolonged blood circulation and active tumor targeting. The precisely controlled NIR irradiation on tumor lesions excites ICG and deforms the cumulated nanogels to trigger burst drug release for facilitated BBB permeation and infiltration into distal tumor cells. These NIR-activatable biomimetic nanogels suppress the tumor growth in orthotopic GBM and GBM stem cells-bearing mouse models with significantly extended survival.

Raman Spectroscopy for Chemical Biology Research

In chemical biology research, various fluorescent probes have been developed and used to visualize target proteins or molecules in living cells and tissues, yet there are limitations to this technology, such as the limited number of colors that can be detected simultaneously. Recently, Raman spectroscopy has been applied in chemical biology to overcome such limitations. Raman spectroscopy detects the molecular vibrations reflecting the structures and chemical conditions of molecules in a sample and was originally used to directly visualize the chemical responses of endogenous molecules. However, our initial research to develop "Raman tags" opens a new avenue for the application of Raman spectroscopy in chemical biology. In this Perspective, we first introduce the label-free Raman imaging of biomolecules, illustrating the biological applications of Raman spectroscopy. Next, we highlight the application of Raman imaging of small molecules using Raman tags for chemical biology research. Finally, we discuss the development and potential of Raman probes, which represent the next-generation probes in chemical biology.

Miniaturized Chemical Tags for Optical Imaging

Recent advances in optical bioimaging have prompted the need for minimal chemical reporters that can retain the molecular recognition properties and activity profiles of biomolecules. As a result, several methodologies to reduce the size of fluorescent and Raman labels to a few atoms (e.g., single aryl fluorophores, Raman-active triple bonds and isotopes) and embed them into building blocks (e.g., amino acids, nucleobases, sugars) to construct native-like supramolecular structures have been described. The integration of small optical reporters into biomolecules has also led to smart molecular entities that were previously inaccessible in an expedite manner. In this article, we review recent chemical approaches to synthesize miniaturized optical tags as well as some of their multiple applications in biological imaging.

High-Resolution Low-Power Hyperspectral Line-Scan Imaging of Fast Cellular Dynamics Using Azo-Enhanced Raman Scattering Probes

Small-molecule Raman probes for cellular imaging have attracted great attention owing to their sharp peaks that are sensitive to environmental changes. The small cross section of molecular Raman scattering limits dynamic cellular Raman imaging to expensive and complex coherent approaches that acquire single-channel images and lose hyperspectral Raman information. We introduce a new method, dynamic azo-enhanced Raman imaging (DAERI), to couple the new class of azo-enhanced Raman probes with a high-speed line-scan Raman imaging system. DAERI achieved high-resolution low-power imaging of fast cellular dynamics resolved at ∼270 nm along the confocal direction, 75 μW/μm² and 3.5 s/frame. Based on the azo-enhanced Raman probes with characteristic signals 10²-10⁴ stronger than classic Raman labels, DAERI was not restricted to the cellular Raman-silent region as in prior work and enabled multiplex visualization of organelle motions and interactions. We anticipate DAERI to be a powerful tool for future studies in biophysics and cell biology.

Reactive oxygen species-responsive and Raman-traceable hydrogel combining photodynamic and immune therapy for postsurgical cancer treatment

Combining immune checkpoint blockade (ICB) therapy with photodynamic therapy (PDT) holds great potential in treating immunologically "cold" tumors, but photo-generated reactive oxygen species (ROS) can inevitably damage co-administered ICB antibodies, hence hampering the therapeutic outcome. Here we create a ROS-responsive hydrogel to realize the sustained co-delivery of photosensitizers and ICB antibodies. During PDT, the hydrogel skeleton poly(deca-4,6-diynedioic acid) (PDDA) protects ICB antibodies by scavenging the harmful ROS, and at the same time, triggers the gradual degradation of the hydrogel to release the drugs in a controlled manner. More interestingly, we can visualize the ROS-responsive hydrogel degradation by Raman imaging, given the ultrastrong and degradation-correlative Raman signal of PDDA in the cellular silent window. A single administration of the hydrogel not only completely inhibits the long-term postoperative recurrence and metastasis of 4T1-tumor-bearing mice, but also effectively restrains the growth of re-challenged tumors. The PDDA-based ROS-responsive hydrogel herein paves a promising way for the durable synergy of PDT and ICB therapy.

Bringing Vibrational Imaging to Chemical Biology with Molecular Probes

As an emerging optical imaging modality, stimulated Raman scattering (SRS) microscopy provides invaluable opportunities for chemical biology studies using its rich chemical information. Through rapid progress over the past decade, the development of Raman probes harnessing the chemical biology toolbox has proven to play a key role in advancing SRS microscopy and expanding biological applications. In this perspective, we first discuss the development of biorthogonal SRS imaging using small tagging of triple bonds or isotopes and highlight their unique advantages for metabolic pathway analysis and microbiology investigations. Potential opportunities for chemical biology studies integrating small tagging with SRS imaging are also proposed. We next summarize the current designs of highly sensitive and super-multiplexed SRS probes, as well as provide future directions and considerations for next-generation functional probe design. These rationally designed SRS probes are envisioned to bridge the gap between SRS microscopy and chemical biology research and should benefit their mutual development.