arXiv subjects

Ji-Xin Cheng

Publications and source records attributed to Ji-Xin Cheng.

39 records · Page 3Linked to original sources

arXiv2019

Plasmon-enhanced Stimulated Raman Scattering Microscopy with Single-molecule Detection Sensitivity

Stimulated Raman scattering (SRS) microscopy allows for high-speed label-free chemical imaging of biomedical systems. The imaging sensitivity of SRS microscopy is limited to ~10 mM for endogenous biomolecules. Electronic pre-resonant SRS allows detection of sub-micromolar chromophores. However, label-free SRS detection of single biomolecules having extremely small Raman cross-sections (~10-30 cm2 sr-1) remains unreachable. Here, we demonstrate plasmon-enhanced stimulated Raman scattering (PESRS) microscopy with single-molecule detection sensitivity. Incorporating pico-Joule laser excitation, background subtraction, and a denoising algorithm, we obtained robust single-pixel SRS spectra exhibiting the statistics of single-molecule events. Single-molecule detection was verified by using two isotopologues of adenine. We further demonstrated the capability of applying PESRS for biological applications and utilized PESRS to map adenine released from bacteria due to starvation stress. PESRS microscopy holds the promise for ultrasensitive detection of molecular events in chemical and biomedical systems.

physics.optics↗

arXiv2018

Bond-Selective Transient Phase Microscopy

Phase-contrast microscopy converts the optical phase introduced by transparent, unlabeled specimens into modulation in the intensity image. Modern phase imaging techniques are capable of quantifying phase shift at each point in the field of view, enabling non-destructive applications in materials and life sciences. However, these attractive features come with the lack of molecular information. To fulfill this gap, we developed a bond-selective transient phase (BSTP) microscope using infrared absorption to excite molecular vibration, resulting in an optical phase change detected through a customized phase microscope. By using pulsed pump and probe lasers, we realized BSTP imaging with high spectral fidelity, sub-microsecond temporal resolution, submicron spatial resolution at 50 frames per second, limited only by the camera sensor. Our approach links the missing molecular bond information to the quantitative phase, which paves a new avenue for spectroscopic imaging in biology and materials science.

physics.optics↗

arXiv2018

Ultrafast Chemical Imaging by Widefield Photothermal Sensing of Infrared Absorption

Infrared (IR) imaging has become a viable tool for visualizing various chemical bonds in a specimen. The performance, however, is limited in terms of spatial resolution and imaging speed. Here, instead of measuring the loss of the IR beam, we utilize a pulsed visible light for a high-throughput, widefield sensing of the transient photothermal effect induced by absorption of single mid-IR pulses. To extract such transient signals, we built a virtual lock-in camera synchronized to the visible probe and IR light pulses with precisely-controlled delays, allowing sub-microsecond temporal resolution determined by the probe pulse width. Our widefield photothermal sensing (WPS) microscope enabled chemical imaging at a speed up to 1250 frames per second, with high spectral fidelity, and offering sub-micron spatial resolution. With the capability of imaging living cells and nanometer-scale polymer films, WPS microscopy opens a new way for high-throughput characterization of biological and material specimens.

physics.optics↗