Photoacoustic microscopy (PAM) enables the measurement of properties associated with optical absorption within tissues and complements sophisticated technologies employing optical microscopy. An inadequate frequency response as determined by a piezoelectric ultrasonic transducer results, however, in poor depth resolution and inaccurate measurements of the coefficients of optical absorption. We developed a PAM system configured as an attenuated total reflectance sensor with a ten-layer graphene film sandwiched between a prism and water (the coupling medium) for photoacoustic (PA) wave detection. Transients of the PA pressure cause perturbations in the refractive index of the water thereby changing the polarization-dependent absorption of the graphene film. The signal in PA detection involves recording the difference in the temporal-varying reflectance intensity between the two orthogonally polarized probe beams. The graphene-based sensor has an estimated noise-equivalent-pressure sensitivity of ∼550 Pa over an approximately linear pressure response from 11.0 kPa to 55.0 kPa. Moreover, it enables a much broader PA bandwidth detection of up to ∼150 MHz, primarily dominated by a highly localized evanescent field. From the strong optical absorption of inherent hemoglobin, in vivo label-free PAM imaging provided a three-dimensional viewing of the microvasculature of a mouse ear. These results suggest great potential for graphene-based PAM in biomedical investigations, such as microcirculation studies.

Photoacoustic microscopy (PAM) can measure optical absorption-based molecular specificities within tissues. Despite the diffraction-limited lateral resolution in optical-resolution photoacoustic microscopy (OR-PAM), the ongoing challenge is poor axial resolution because of an insufficient ultrasound detection bandwidth, which hampers PAM volumetric imaging. We propose polarization-differential surface plasmon resonance (SPR) sensing for broadband and highsensitivity photoacoustic (PA) detection, allowing OR-PAM with comparable resolution along lateral and axial directions. This sensor possesses an estimated noise-equivalent-pressure sensitivity of ∼477 Pa over an approximately linear pressure response up to 107 kPa. Moreover, an improved PA detection bandwidth of ∼173 MHz permits an axial resolution (∼7.6 μm) that approaches the lateral resolution (∼4.5 μm) of our OR-PAM system. The capability in spatially isometric micrometer-scale resolution enables in vivo volumetric label-free imaging of the microvasculature of a mouse ear. The SPR sensing technology promises broader applications of PAM in biomedical studies such as microcirculation.

We propose an all-optical technique for plasmonic structured illumination microscopy (PSIM) with perfect optical vortex (POV). POV can improve the efficiency of the excitation of surface plasma and reduce the background noise of the excited fluorescence. The plasmonic standing wave patterns are excited by POV with fractional topological charges for accurate phase shift of {−2π/3, 0, and 2π/3}. The imaging resolution of less than 200 nm was produced. This PSIM technique is expected to be used as a wide field, super resolution imaging technique in dynamic biological imaging.

This study shows that convolutional neural networks (CNNs) can be used to improve the performance of structured illumination microscopy to enable it to reconstruct a super-resolution image using three instead of nine raw frames, which is the standard number of frames required to this end. Owing to the isotropy of the fluorescence group, the correlation between the high-frequency information in each direction of the spectrum is obtained by training the CNNs. A high-precision super-resolution image can thus be reconstructed using accurate data from three image frames in one direction. This allows for gentler super-resolution imaging at higher speeds and weakens phototoxicity in the imaging process.

Relying on high-sensitivity refractive index sensing and a highly constrained evanescent field of surface plasmon resonance (SPR), broadband photoacoustic (PA) pressure transients were measured using an SPR sensor instead of routinely used piezoelectric ultrasonic transducers. An acoustic cavity made from stainless steel and having a designed ellipsoidal inner surface redirected laser-induced PA waves from the PA excitation spot to the SPR sensor. By incorporating the SPR sensor with the acoustic cavity, we developed optical-resolution photoacoustic microscopy (OR-PAM) with multiple advantages, including reflection-mode signal capture, improved PA detection sensitivity, increased PA spectral bandwidth as broad as ∼98 MHz, and micrometer-scale lateral resolution. This allowed label-free volumetric PA imaging of vasculature in not only the thin ear but also the thick forelimb of living mice. With these combined advantages, our OR-PAM system potentially offers more opportunities for biomedical investigation, for example, when studying microcirculations in the eye and cortex.