Stimulated Raman scattering microscopy and spectroscopy with a rapid scanning optical delay line

Agile acousto-optic delay line for fast impulsive stimulated Raman imaging

We introduce and characterize a fast (50 kHz), long range (50 ps) and random-access optical delay line based on an acousto-optic deflector inserted in the Fourier plane of a zero-dispersion line. The advantages of this agile delay line are demonstrated in the context of impulsive stimulated Raman imaging in the low-frequency range (<200 cm-1). Besides fast imaging with a spectral resolution of 1.5 cm-1, we show that random-access delay may be exploited to selectively image molecular species at high speed.

Widely tunable fiber optical parametric oscillator synchronized with a Ti:sapphire laser for stimulated Raman scattering microscopy

Stimulated Raman scattering (SRS) microscopy is a powerful vibrational imaging technique with high chemical specificity. However, the insufficient tuning range or speed of light sources limits the spectral range of SRS imaging and, hence, the ability to identify molecular species. Here, we present a widely tunable fiber optical parametric oscillator with a tuning range of 1470 cm-1, which can be synchronized with a Ti:sapphire laser. By using the synchronized light sources, we develop an SRS imaging system that covers the fingerprint and C-H stretching regions, without balanced detection. We validate its broadband imaging capability by visualizing a mixed polymer sample in multiple vibrational modes. We also demonstrate SRS imaging of HeLa cells, showing the applicability of our SRS microscope to biological samples.

Reviews of bio-orthogonal probes in bioscience by stimulated Raman scattering microscopy

Stimulated Raman scattering (SRS) microscopy, is a nonlinear optical imaging method for visualizing chemical content based on molecular vibrational bonds, with high sensitivity, resolution, speed, and specificity. In the current review, we provided a comprehensive and critical review of the most recent developments in the field of SRS in combination with bio-orthogonal Raman tags or labels in bioscience. Firstly, we introduced the fundamentals of SRS microscopy and the theory principle of bio-orthogonal Raman tags. In particular, present the applications of each kind of bio-orthogonal Raman tags, including heavy water (D2O), stable isotope probes (SIP), and triple-bonds tags. And shared our vision for the remaining challenges, research needs, and potential future breakthroughs for SRS technology lastly. We envision that the advanced SRS imaging and analysis will be a major force in future biological discovery.

Stimulated Raman Scattering Imaging Sheds New Light on Lipid Droplet Biology

A lipid droplet (LD) is a dynamic organelle closely associated with cellular functions and energy homeostasis. Dysregulated LD biology underlies an increasing number of human diseases, including metabolic disease, cancer, and neurodegenerative disorder. Commonly used lipid staining and analytical tools have difficulty providing the information regarding LD distribution and composition at the same time. To address this problem, stimulated Raman scattering (SRS) microscopy uses the intrinsic chemical contrast of biomolecules to achieve both direct visualization of LD dynamics and quantitative analysis of LD composition with high molecular selectivity at the subcellular level. Recent developments of Raman tags have further enhanced sensitivity and specificity of SRS imaging without perturbing molecular activity. With these advantages, SRS microscopy has offered great promise for deciphering LD metabolism in single live cells. This article overviews and discusses the latest applications of SRS microscopy as an emerging platform to dissect LD biology in health and disease.

Spectral imaging at high definition and high speed in the mid-infrared

Spectral imaging in the mid-infrared (MIR) range provides simultaneous morphological and chemical information of a wide variety of samples. However, current MIR technologies struggle to produce high-definition images over a broad spectral range at acquisition rates that are compatible with real-time processes. We present a novel spectral imaging technique based on nondegenerate two-photon absorption of temporally chirped optical MIR pulses. This approach avoids complex image processing or reconstruction and enables high-speed acquisition of spectral data cubes (xyω) at high-pixel density in under a second.

Broadband stimulated Raman imaging based on multi-channel lock-in detection for spectral histopathology

Spontaneous Raman microscopy reveals the chemical composition of a sample in a label-free and non-invasive fashion by directly measuring the vibrational spectra of molecules. However, its extremely low cross section prevents its application to fast imaging. Stimulated Raman scattering (SRS) amplifies the signal by several orders of magnitude thanks to the coherent nature of the nonlinear process, thus unlocking high-speed microscopy applications that provide analytical information to elucidate biochemical mechanisms with subcellular resolution. Nevertheless, in its standard implementation, narrowband SRS provides images at only one frequency at a time, which is not sufficient to distinguish constituents with overlapping Raman bands. Here, we report a broadband SRS microscope equipped with a home-built multichannel lock-in amplifier simultaneously measuring the SRS signal at 32 frequencies with integration time down to 44 µs, allowing for detailed, high spatial resolution mapping of spectrally congested samples. We demonstrate the capability of our microscope to differentiate the chemical constituents of heterogeneous samples by measuring the relative concentrations of different fatty acids in cultured hepatocytes at the single lipid droplet level and by differentiating tumor from peritumoral tissue in a preclinical mouse model of fibrosarcoma.

Fiber-Enhanced Stimulated Raman Scattering and Sensitive Detection of Dilute Solutions

Stimulated Raman scattering (SRS) is known to gain coherent amplification of molecular vibrations that allow for rapid and label-free chemical imaging in the microscopy setting. However, the tightly focused laser spot has limited the detection sensitivity, partly due to the tiny interaction volume. Here, we report the use of metal-lined hollow-core fiber (MLHCF) to improve the sensitivity of SRS in sensing dilute solutions by extending the light-matter interaction volume through the fiber waveguide. With a focusing lens (100 mm FL) and 320 μm diameter fiber, we demonstrated an optimum enhancement factor of ~20 at a fiber length of 8.3 cm. More importantly, the MLHCF exhibited a significantly suppressed cross-phase modulation (XPM) background, enabling the detection of ~0.7 mM DMSO in water. Furthermore, the relationship between fiber length and SRS signal could be well explained theoretically. The fiber-enhanced SRS (FE-SRS) method may be further optimized and bears potential in the sensitive detection of molecules in the solution and gas phases.

Label-free skin penetration analysis using time-resolved, phase-modulated stimulated Raman scattering microscopy

Skin penetration analysis of topically applied drugs or active compounds is essential in biomedical applications. Stimulated Raman scattering (SRS) microscopy is a promising label-free skin penetration analysis tool. However, conventional SRS microcopy suffers from limited signal contrast owing to strong background signals, which prevents its use in low-concentration drug imaging. Here, we present a skin penetration analysis method of topical agents using recently developed phase-modulated SRS (PM-SRS) microscopy. PM-SRS uses phase modulation and time-resolved signal detection to suppress both nonlinear background signals and Raman background signals from a tissue. A proof-of-concept experiment with a topically applied skin moisturizing agent (ectoine) in an in vitro skin tissue model revealed that PM-SRS with 1.7-ps probe delay yields a signal contrast 40 times higher than that of conventional amplitude-modulated SRS (AM-SRS). Skin penetration measurement of a topical therapeutic drug (loxoprofen sodium) showed that the mean drug concentration at the tissue surface layer after 240 min was 47.3 ± 4.8 mM. The proposed PM-SRS microscopy can be employed to monitor the spatial and temporal pharmacokinetics of small molecules in the millimolar concentration regime.

Coherent Raman scattering microscopy: capable solution in search of a larger audience

SIGNIFICANCE

Coherent Raman scattering (CRS) microscopy is an optical imaging technique with capabilities that could benefit a broad range of biomedical research studies.

AIM

We reflect on the birth, rapid rise, and inescapable growing pains of the technique and look back on nearly four decades of developments to examine where the CRS imaging approach might be headed in the next decade to come.

APPROACH

We provide a brief historical account of CRS microscopy, followed by a discussion of the challenges to disseminate the technique to a larger audience. We then highlight recent progress in expanding the capabilities of the CRS microscope and assess its current appeal as a practical imaging tool.

RESULTS

New developments in Raman tagging have improved the specificity and sensitivity of the CRS technique. In addition, technical advances have led to CRS microscopes that can capture hyperspectral data cubes at practical acquisition times. These improvements have broadened the application space of the technique.

CONCLUSION

The technical performance of the CRS microscope has improved dramatically since its inception, but these advances have not yet translated into a substantial user base beyond a strong core of enthusiasts. Nonetheless, new developments are poised to move the unique capabilities of the technique into the hands of more users.

Microsecond fingerprint stimulated Raman spectroscopic imaging by ultrafast tuning and spatial-spectral learning

Label-free vibrational imaging by stimulated Raman scattering (SRS) provides unprecedented insight into real-time chemical distributions. Specifically, SRS in the fingerprint region (400-1800 cm-1) can resolve multiple chemicals in a complex bio-environment. However, due to the intrinsic weak Raman cross-sections and the lack of ultrafast spectral acquisition schemes with high spectral fidelity, SRS in the fingerprint region is not viable for studying living cells or large-scale tissue samples. Here, we report a fingerprint spectroscopic SRS platform that acquires a distortion-free SRS spectrum at 10 cm-1 spectral resolution within 20 µs using a polygon scanner. Meanwhile, we significantly improve the signal-to-noise ratio by employing a spatial-spectral residual learning network, reaching a level comparable to that with 100 times integration. Collectively, our system enables high-speed vibrational spectroscopic imaging of multiple biomolecules in samples ranging from a single live microbe to a tissue slice.

Microcalcification-Based Tumor Malignancy Evaluation in Fresh Breast Biopsies with Hyperspectral Stimulated Raman Scattering

Precise evaluation of breast tumor malignancy based on tissue calcifications has important practical value in the disease diagnosis, as well as the understanding of tumor development. Traditional X-ray mammography provides the overall morphologies of the calcifications but lacks intrinsic chemical information. In contrast, spontaneous Raman spectroscopy offers detailed chemical analysis but lacks the spatial profiles. Here, we applied hyperspectral stimulated Raman scattering (SRS) microscopy to extract both the chemical and morphological features of the microcalcifications, based on the spectral and spatial domain analysis. A total of 211 calcification sites from 23 patients were imaged with SRS, and the results were analyzed with a support vector machine (SVM) based classification algorithm. With optimized combinations of chemical and geometrical features of microcalcifications, we were able to reach a precision of 98.21% and recall of 100.00% for classifying benign and malignant cases, significantly improved from the pure spectroscopy or imaging based methods. Our findings may provide a rapid means to accurately evaluate breast tumor malignancy based on fresh tissue biopsies.

Advances in stimulated Raman scattering imaging for tissues and animals

Stimulated Raman scattering (SRS) microscopy has emerged in the last decade as a powerful optical imaging technology with high chemical selectivity, speed, and subcellular resolution. Since the invention of SRS microscopy, it has been extensively employed in life science to study composition, structure, metabolism, development, and disease in biological systems. Applications of SRS in research and the clinic have generated new insights in many fields including neurobiology, tumor biology, developmental biology, metabolomics, pharmacokinetics, and more. Herein we review the advances and applications of SRS microscopy imaging in tissues and animals, as well as envision future applications and development of SRS imaging in life science and medicine.

Highly specific and label-free histological identification of microcrystals in fresh human gout tissues with stimulated Raman scattering

Gout is a common metabolic disease with growing burden, caused by monosodium urate (MSU) microcrystal deposition. In situ and chemical-specific histological identification of MSU is crucial in the diagnosis and management of gout, yet it remains inaccessible for current histological methods. Methods: Stimulated Raman scattering (SRS) microscopy was utilized to image MSU based on its fingerprint Raman spectra. We first tested SRS for the diagnosis capability of gout and the differentiation power from pseudogout with rat models of acute gout arthritis, calcium pyrophosphate deposition disease (CPDD) and comorbidity. Then, human synovial fluid and surgical specimens (n=120) were were imaged with SRS to obtain the histopathology of MSU and collagen fibers. Finally, quantitative SRS analysis was performed in gout tissue of different physiological phases (n=120) to correlate with traditional histopathology including H&E and immunohistochemistry staining. Results: We demonstrated that SRS is capable of early diagnosis of gout, rapid detection of MSU in synovial fluid and fresh unprocessed surgical tissues, and accurate differentiation of gout from pseudogout in various pathophysiological conditions. Furthermore, quantitative SRS analysis revealed the optical characteristics of MSU deposition at different pathophysiological stages, which were found to matched well with corresponding immunofluorescence histochemistry features. Conclusion: Our work demonstrated the potential of SRS microscopy for rapid intraoperative diagnosis of gout and may facilitate future fundamental researches of MSU-based diseases.

Review of Stimulated Raman Scattering Microscopy Techniques and Applications in the Biosciences

Stimulated Raman scattering (SRS) microscopy is a nonlinear optical imaging method for visualizing chemical content based on molecular vibrational bonds. Featuring high speed, high resolution, high sensitivity, high accuracy, and 3D sectioning, SRS microscopy has made tremendous progress toward biochemical information acquisition, cellular function investigation, and label-free medical diagnosis in the biosciences. In this review, the principle of SRS, system design, and data analysis are introduced, and the current innovations of the SRS system are reviewed. In particular, combined with various bio-orthogonal Raman tags, the applications of SRS microscopy in cell metabolism, tumor diagnosis, neuroscience, drug tracking, and microbial detection are briefly examined. The future prospects for SRS microscopy are also shared.

Rapid Determination of Antimicrobial Susceptibility by Stimulated Raman Scattering Imaging of D2O Metabolic Incorporation in a Single Bacterium

Rapid antimicrobial susceptibility testing (AST) is urgently needed for treating infections with appropriate antibiotics and slowing down the emergence of antibiotic-resistant bacteria. Here, a phenotypic platform that rapidly produces AST results by femtosecond stimulated Raman scattering imaging of deuterium oxide (D2O) metabolism is reported. Metabolic incorporation of D2O into biomass in a single bacterium and the metabolic response to antibiotics are probed in as short as 10 min after culture in 70% D2O medium, the fastest among current technologies. Single-cell metabolism inactivation concentration (SC-MIC) is obtained in less than 2.5 h from colony to results. The SC-MIC results of 37 sets of bacterial isolate samples, which include 8 major bacterial species and 14 different antibiotics often encountered in clinic, are validated by standard minimal inhibitory concentration blindly measured via broth microdilution. Toward clinical translation, stimulated Raman scattering imaging of D2O metabolic incorporation and SC-MIC determination after 1 h antibiotic treatment and 30 min mixture of D2O and antibiotics incubation of bacteria in urine or whole blood is demonstrated.

High-speed chemical imaging of dynamic and histological samples with stimulated Raman micro-spectroscopy

We report a shot noise limited high-speed stimulated Raman microscopy platform allowing to acquire molecular vibrational spectra over 200 cm^-1 in 12 µs at a scan rate of 40kHz. Using spectral focusing together with optimized acousto-optics programmable dispersive filters, the designed low noise imaging platform performs chemical imaging of dynamical processes such as Mannitol crystal hydration and reaches a signal to noise ratio sufficient to perform label free histological imaging on frozen human colon tissue slides.

Vibrational Imaging and Quantification of Two-Dimensional Hexagonal Boron Nitride with Stimulated Raman Scattering

Hexagonal boron nitride (h-BN) is an important member of two-dimensional (2D) materials with a large direct bandgap, and has attracted growing interest in ultraviolet optoelectronics and nanoelectronics. Compared with graphene and graphite, h-BN has weak Raman effect because of the far off-resonance excitation; hence, it is difficult to exploit Raman spectroscopy to characterize important properties of 2D h-BN, such as thickness, doping, and strain effects. Here, we applied stimulated Raman scattering (SRS) to enhance the sensitivity of the E_2g Raman mode of h-BN. We showed that SRS microscopy achieves rapid high resolution imaging of h-BN with a pixel dwell time 4 orders of magnitude smaller than conventional spontaneous Raman microscopy. Moreover, the near-perfect linear dependence of signal intensity on h-BN thickness and isotropic polarization dependence allow convenient determination of the flake thickness with SRS imaging. Our results indicated that SRS microscopy provides a promising tool for high-speed quantification of h-BN and holds the potential for vibrational imaging of 2D materials.

Biological imaging of chemical bonds by stimulated Raman scattering microscopy

All molecules consist of chemical bonds, and much can be learned from mapping the spatiotemporal dynamics of these bonds. Since its invention a decade ago, stimulated Raman scattering (SRS) microscopy has become a powerful modality for imaging chemical bonds with high sensitivity, resolution, speed and specificity. We introduce the fundamentals of SRS microscopy and review innovations in SRS microscopes and imaging probes. We highlight examples of exciting biological applications, and share our vision for potential future breakthroughs for this technology.

Label-free chemical imaging flow cytometry by high-speed multicolor stimulated Raman scattering

Imaging flow cytometry is a powerful tool for analyzing every single cell in a large heterogeneous population but relies on fluorescent labeling, which comes with cytotoxicity, nonspecific binding, and interference with natural cellular functions. This paper presents label-free multicolor chemical imaging flow cytometry based on stimulated Raman scattering (SRS), a highly sensitive method of molecular vibrational spectroscopy. With the help of deep learning, it demonstrates high-precision characterization and classification of microalgal cells and cancer cells without the need for fluorescent labeling.

Combining the strength of flow cytometry with fluorescence imaging and digital image analysis, imaging flow cytometry is a powerful tool in diverse fields including cancer biology, immunology, drug discovery, microbiology, and metabolic engineering. It enables measurements and statistical analyses of chemical, structural, and morphological phenotypes of numerous living cells to provide systematic insights into biological processes. However, its utility is constrained by its requirement of fluorescent labeling for phenotyping. Here we present label-free chemical imaging flow cytometry to overcome the issue. It builds on a pulse pair-resolved wavelength-switchable Stokes laser for the fastest-to-date multicolor stimulated Raman scattering (SRS) microscopy of fast-flowing cells on a 3D acoustic focusing microfluidic chip, enabling an unprecedented throughput of up to ∼140 cells/s. To show its broad utility, we use the SRS imaging flow cytometry with the aid of deep learning to study the metabolic heterogeneity of microalgal cells and perform marker-free cancer detection in blood.

Volumetric chemical imaging by clearing-enhanced stimulated Raman scattering microscopy

Three-dimensional visualization of tissue structures using optical microscopy facilitates the understanding of biological functions. However, optical microscopy is limited in tissue penetration due to severe light scattering. Recently, a series of tissue-clearing techniques have emerged to allow significant depth-extension for fluorescence imaging. Inspired by these advances, we develop a volumetric chemical imaging technique that couples Raman-tailored tissue-clearing with stimulated Raman scattering (SRS) microscopy. Compared with the standard SRS, the clearing-enhanced SRS achieves greater than 10-times depth increase. Based on the extracted spatial distribution of proteins and lipids, our method reveals intricate 3D organizations of tumor spheroids, mouse brain tissues, and tumor xenografts. We further develop volumetric phasor analysis of multispectral SRS images for chemically specific clustering and segmentation in 3D. Moreover, going beyond the conventional label-free paradigm, we demonstrate metabolic volumetric chemical imaging, which allows us to simultaneously map out metabolic activities of protein and lipid synthesis in glioblastoma. Together, these results support volumetric chemical imaging as a valuable tool for elucidating comprehensive 3D structures, compositions, and functions in diverse biological contexts, complementing the prevailing volumetric fluorescence microscopy.

Quantitative imaging of lipid droplets in single cells

The combination of next generation sequencing (NGS) and automated liquid handling platforms has led to a revolution in single-cell genomic studies. However, many molecules that are critical to understanding the functional roles of cells in a complex tissue or organs, are not directly encoded in the genome, and therefore cannot be profiled with NGS. Lipids, for example, play a critical role in many metabolic processes but cannot be detected by sequencing. Recent developments in quantitative imaging, particularly coherent Raman scattering (CRS) techniques, have produced a suite of tools for studying lipid content in single cells. This article reviews CRS imaging and computational image processing techniques for non-destructive profiling of dynamic changes in lipid composition and spatial distribution at the single-cell level. As quantitative CRS imaging progresses synergistically with microfluidic and microscopic platforms for single-cell genomic analysis, we anticipate that these techniques will bring researchers closer towards combined lipidomic and genomic analysis.

Label-free imaging of amyloid plaques in Alzheimer's disease with stimulated Raman scattering microscopy

One of the key pathological features of Alzheimer's disease (AD) is the existence of extracellular deposition of amyloid plaques formed with misfolded amyloid-β (Aβ). The conformational change of proteins leads to enriched contents of β sheets, resulting in remarkable changes of vibrational spectra, especially the spectral shifts of the amide I mode. Here, we applied stimulated Raman scattering (SRS) microscopy to image amyloid plaques in the brain tissue of an AD mouse model. We have demonstrated the capability of SRS microscopy as a rapid, label-free imaging modality to differentiate misfolded from normal proteins based on the blue shift (~10 cm^-1) of amide I SRS spectra. Furthermore, SRS imaging of Aβ plaques was verified by antibody staining of frozen thin sections and fluorescence imaging of fresh tissues. Our method may provide a new approach for studies of AD pathology, as well as other neurodegenerative diseases associated with protein misfolding.

Pulse length variation causing spectral distortions in OPO-based hyperspectral coherent Raman scattering microscopy

Picosecond optical parametric oscillators (OPOs) with broad wavelength tunability are frequently used as light sources in hyperspectral coherent Raman scattering (CRS) microscopy. We investigate how changes in the pulse length during OPO wavelength tuning of the pump beam affect hyperspectral CRS imaging. We find that significant distortions of the resulting CRS spectra occur if the OPO is operated without monitoring pulse length variations. By utilizing a custom-written MATLAB based control program to counteract changes in pulse length, normalized and reproducible data sets can be acquired. We demonstrate this by comparing hyperspectral data obtained from pure substances, as well as relevant biological specimens.

Label-free imaging of hemoglobin degradation and hemosiderin formation in brain tissues with femtosecond pump-probe microscopy

The degradation of hemoglobin in brain tissues results in the deposition of hemosiderin, which is a major form of iron-storage protein and closely related to neurological disorders such as epilepsy. Optical detection of hemosiderin is vitally important yet challenging for the understanding of disease mechanisms, as well as improving surgical resection of brain lesions. Here, we provide the first label-free microscopy study of sensitive hemosiderin detection in both an animal model and human brain tissues. Methods: We applied spectrally and temporally resolved femtosecond pump-probe microscopy, including transient absorption (TA) and stimulated Raman scattering (SRS) techniques, to differentiate hemoglobin and hemosiderin in brain tissues. The label-free imaging results were compared with Perls' staining to evaluate our method for hemosiderin detection. Results: Significant differences between hemoglobin and hemosiderin transient spectra were discovered. While a strong ground-state bleaching feature of hemoglobin appears in the near-infrared region, hemosiderin demonstrates pure excited-state absorption dynamics, which could be explained by our proposed kinetic model. Furthermore, simultaneous imaging of hemoglobin and hemosiderin can be rapidly achieved in both an intracerebral hemorrhage (ICH) rat model and human brain surgical specimens, with perfect correlation with Perls' staining. Conclusion: Our results suggest that rapid, label-free detection of hemosiderin in brain tissues could be realized by femtosecond pump-probe microscopy. Our method holds great potential in providing a new tool for intraoperative detection of hemosiderin during brain surgeries.

Rapid, large-scale stimulated Raman histology with strip mosaicing and dual-phase detection

Two-color stimulated Raman scattering (SRS) microscopy with label-free mapping of lipid/protein distributions has shown promise in virtual histology. Despite previous demonstrations of SRS in tumor delineation and diagnosis, the speed and efficiency of the current technique requires further improvements for practical use. Here, we integrate parallel dual-phase SRS detection with strip mosaicing, which reduces the imaging time of a whole mouse brain section from 70 to 8 minutes. We further verified our method in imaging fresh human surgical tissues, showing its great potential for rapid SRS histology, especially for large scale, large quantity imaging tasks.

Imaging Laser-Triggered Drug Release from Gold Nanocages with Transient Absorption Lifetime Microscopy

Nanoparticles have shown promise in loading and delivering drugs for targeted therapy. Many progresses have been made in the design, synthesis, and modification of nanoparticles to fulfill such goals. However, realizing targeted intracellular delivery and controlled release of drugs remains challenging, partly because of the lack of reliable tools to detect the drug-releasing process. In this paper, we applied femtosecond laser pulses to trigger the explosion of gold nanocages (AuNCs) and control the intracellular release of loaded aluminum phthalocyanine (AlPcS) molecules for photodynamic therapy (PDT). AuNCs were found to enhance the encapsulation efficiency and suppress the PDT effect of AlPcS molecules until they were released. More importantly, we discovered that the excited-state lifetimes of the AlPcS-AuNC conjugate (∼3 ps) and free AlPcS (∼11 ps) differ significantly, which was utilized to image the released drug molecules using transient absorption lifetime microscopy with the same laser source. This technique extracts information similar to fluorescence lifetime imaging microscopy but is superior in imaging the molecules that hardly fluoresce or are prone to photobleaching. We further combined a dual-phase lock-in detection technique to show the potential of real-time imaging based on the change in transient optical behaviors. Our method may provide a new tool for investigating nanoparticle-assisted drug delivery and release.

High-speed stimulated hyperspectral Raman imaging using rapid acousto-optic delay lines

Stimulated Raman scattering (SRS) is a powerful, label-free imaging technique that holds significant potential for medical imaging. To allow chemical specificity and minimize spectral distortion in the imaging of live species, a high-speed multiplex SRS imaging platform is needed. By combining a spectral focusing excitation technique with a rapid acousto-optic delay line, we demonstrate a hyperspectral SRS imaging platform capable of measuring a 3-dB spectral window of ∼200  cm^-1 within 12.8 μs with a scan rate of 30 KHz. We present hyperspectral images of a mixture of two different microsphere polymers as well as live fungal cells mixed with human blood.