We present a novel version of mid-infrared photothermal microscopy in which thermosensitive fluorescent probes are harnessed to sense the mid-infrared photothermal effect. The fluorescence intensity can be modulated at the level of 1% per Kelvin, which is 100 times larger than the modulation of scattering intensity. In addition, fluorescence emission is free of interference, thus much improving the image quality. Moreover, fluorophores can target specific organelles or biomolecules, thus augmenting the specificity of photothermal imaging. Spectral fidelity is confirmed by fingerprinting a single bacterium. A wide-field fluorescence-detected mid-infrared photothermal microscope developed allows video-rate bond-selective imaging of biological specimens.
Mid-infrared photothermal (MIP) imaging is an emerging technique where a visible beam is deployed to sense the photothermal lensing effect induced by infrared absorption of molecules. This technology provides sub-micron spatial resolution defined by the visible probe beam. Yet, the photothermal lensing effect is a weak effect for most materials. For instance, the diffraction coefficient of poly (methyl methacrylate) changes around 0.1% per Kelvin. Thus, highly sensitive probes are desired to improve the detection sensitivity. Here, we report a fluorescence-enhanced mid-infrared photothermal (FE-MIP) microscope with high sensitivity. MIP microscopy uses a pump-probe strategy in which a mid-infrared light vibrationally excites a sample and a visible light probes the thermal effect. Instead of measuring the scattering modulated by mid-infrared absorption, we deploy thermal sensitive fluorescent dyes as the probe, and measure the modulated fluorescence intensity in both confocal mode and wide field mode. We demonstrate high imaging sensitivity and component specificity through fluorescence labeling.
This work demonstrates a rapid platform that can determine the antimicrobial susceptibility testing (AST) in cation-adjusted Mueller-Hinton Broth medium, urine and blood by stimulated Raman scattering (SRS) imaging of deuterium oxide (D2O) incorporation at a single bacterium level. The total AST assay time with the value of the single-cell metabolism inactivation concentration (SC-MIC) obtained is less than 2.5 h from colony to results. The SC-MIC results of 37 sets of bacterial isolate samples were systematically validated by MIC determined by the Clinical and Laboratory Standards Institute criteria, with a category agreement of 94.6% and 5.4% minor error. Furthermore, SRS imaging of D2O metabolic incorporation can rapidly determine SC-MIC directly in clinical samples for urinary tract infection or septicemia blood infection.
The rapid evolution of antibiotic resistance increasingly challenges the successful treatment of S. aureus infections. Here, we present an unconventional treatment approach by disassembly its membrane microdomains via pulsed laser photolysis of staphyloxanthin. After staphyloxanthin photolysis, membrane permeabilization, fluidification, and membrane protein detachment, were found the underlying mechanisms to malfunction its defense to several major classes of conventional antibiotics. Through resistance selection study, we found pulsed laser treatment completely depleted staphyloxanthin virulence. More importantly, laser treatment further inhibited development of resistance for several major classes of conventional antibiotics including fluoroquinolones, tetracyclines, aminoglycosides, and oxazolidinones. Collectively, this work highlights a novel platform to revive conventional antibiotics to treat S. aureus infections.
KEYWORDS: Crystals, Microscopy, Absorption, Raman spectroscopy, Blood, Scanning electron microscopy, Signal to noise ratio, In vitro testing, Chemical analysis, Imaging spectroscopy
Hemozoin, the heme detoxification end product in malaria parasites during their growth in the red blood cells (RBCs), serves as an important marker for diagnosis and treatment target of malaria disease. However, the current method for hemozoin-targeted drug screening mainly relies on in-vitro β-hematin inhibition assays, which may lead to false-positive events due to under-representation of the real hemozoin crystal. Quantitative in-situ imaging of hemozoin is highly desired for high-throughput screening of antimalarial drugs and for elucidating the mechanisms of antimalarial drugs. We present transient absorption (TA) imaging as a high-speed single-cell analysis platform with chemical selectivity to hemozoin. We first demonstrated that TA microscopy is able to identify β-hematin, the artificial form of hemozoin, from the RBCs. We further utilized time-resolved TA imaging to in situ discern hemozoin from malaria-infected RBCs with optimized imaging conditions. Finally, we quantitatively analyzed the hemozoin amount in RBCs at different infection stages by single-shot TA imaging. These results highlight the potential of TA imaging for efficient antimalarial drug screening and drug mechanism investigation.
The prevalence of antibiotic resistance and the presence of bacterial persisters increasingly challenge the successful treatment of Staphylococcus aureus infections, and thus poses a great threat to the global health. Here, we present a photonic approach to revive a broad spectrum of antibiotics for eradication of MRSA persisters via photo-disassembly of functional membrane microdomains. Membrane microdomains on MRSA cells are enriched in staphyloxanthin-derived lipids as constituent lipids with co-localized and oligomerized multimeric protein complexes including PBP2a to execute various cellular processes and cell virulence. We demonstrated that the membrane-bound staphyloxinthin is prone to photobleaching by blue light due to triplet-triplet annihilation and thus compromises the membrane integrity. Using high-intensity 460 nm pulsed laser (wide-field illumination, dosage far below human safety limit), we achieved strikingly high staphyloxanthin bleaching efficiency and depth when compared to low-level light sources (quantified by resonance Raman spectroscopy). More importantly, such efficient and selective photolysis of constituent lipids leads to catastrophic disassembly of membrane microdomains, yielding highly compromised cell membrane with nanometer-scale pores created and PBP2a unanchored from cell membrane or dispersed (proved and quantified by immunofluorescence, fluorescence assay, confocal, super-resolution imaging, and Western blotting). The disruption renders MRSA persisters highly traumatized, thus no longer in dormant state (verified by stimulated Raman scattering microscopy). Consequently, cells with compromised membrane are found highly susceptible to a broad spectrum of antibiotics: beta-lactam antibiotics, such as penicillin and cephalosporins, due to PBP2a disassembly; antibiotics that inhibit intracellular activities enabled by effective diffusion via nanometer-scale pores, such as quinolones, aminoglycosides and sulfonamides. These synergistic therapies are validated both in vitro and in clinically relative models including biofilm and mice skin infection model. Collective, our findings unveil the underlying mechanism of photo-disassembly of MRSA membrane microdomains and highlight this photonic approach as a novel platform to revive a broad spectrum of conventional antibiotics and guide the development of new antibiotics for treatment of MRSA infections.
Spectroscopic stimulated Raman scattering (SRS) is a label-free chemical imaging modality enabling visualization of molecules in living systems with high specificity. Among various spectroscopic SRS imaging methods, a convenient way is through linearly chirping two femtosecond lasers and tuning their temporal delay, which in turn corresponds to different Raman shifts. Currently, the acquisition speed using a resonant mirror is 3 seconds (80 microseconds per spectrum), which is insufficient for imaging samples with high motility. In this work, we aim to push the imaging speed using a 50-kHz polygon scanner as a delay line tuner, achieving a speed of 20 microseconds per spectrum. At such high speeds, to overcome the signal level decrease due to reduced signal integration time, we apply a U-Net deep learning framework, which first takes pairs of spectroscopic SRS images at different speeds as training samples, with high-speed, low-signal images as input and low speed, high-signal ones as output. After training, the network is capable of rapidly transforming a low-signal spectroscopic image to a high-signal version. Consequently, our design can generate ultrafast spectroscopic SRS image while maintaining the signal level comparable to the output with longer signal integration time.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.