Fiber lasers have transformed microscopy with their robustness and portability. Fiber laser-based stimulated Raman scattering (SRS) offers label-free chemical imaging but faces challenges like noise and high light collection requirements. To overcome these, we introduce stimulated Raman photothermal (SRP) microscopy with fiber lasers. SRP detects thermal effects induced by SRS, reducing sensitivity to laser noise and eliminating balance detection needs. Our setup allows light collection through a low NA air condenser, simplifying operation for non-experts. SRP demonstrates superior sensitivity, particularly in media with high thermos-optic coefficients, outperforming fiber laser-based SRS. We showcase SRP's efficacy in imaging biological samples, promising enhanced sensitivity, resolution, and user-friendliness. This innovation signifies a significant step forward in biological microscopy, offering potential for widespread adoption and groundbreaking discoveries in vibrational imaging.
Retina prosthesis are implantable devices stimulating diseased retina of individuals to restore vision. New technologies are needed for precise and non-genetic retinal stimulation. Here we report the development of different photoacoustic platforms for retina stimulation. First, we demonstrated that a tapered fiber based photoacoustic emitter consistently evokes action potentials with response patterns that are sensitive to the stimulus waveform using patch clamp recordings in a retinal explant. Second, toward the implantable retinal prothesis, we confirmed successful blind retina stimulation through a PDMS-based photoacoustic film safely. These results show the potential of using optoacoustic signal to drive activity in photoreceptor-damaged retinas.
Microwaves, which have a ∼10-cm wavelength, can penetrate deeper into tissue than photons, heralding exciting deep tissue applications such as modulation or imaging via the thermoacoustic effect. Thermoacoustic conversion efficiency is however very low, even with an exogenous contrast agent. We break this low-conversion limit, using a split ring resonator to effectively collect and confine the microwaves into a submillimeter hot spot for ultrasound emission and achieve a conversion efficiency over 2000 times higher than other reported thermoacoustic contrast agents. Importantly, the frequency of emitted ultrasound can be precisely tuned and multiplexed by modulation of the microwave pulses. Such performance is inaccessible by a piezoelectric-based transducer or a photoacoustic emitter and, therefore, split ring resonators open up new opportunities to study the frequency response of cells in ultrasonic biomodulation. For applications in deep tissue localization, a split ring resonator can be used as a wireless, battery-free ultrasound beacon placed under a breast phantom.
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