Photoacoustic (PA) imaging holds great promise for preclinical research and clinical practice. However, most studies rely on the laser wavelength in the first near-infrared (NIR) window (NIR-I, 650–950 nm), while few studies have been exploited in the second NIR window (NIR-II, 1000–1700 nm), mainly due to the lack of NIR-II absorbing contrast agents. We herein report the synthesis of a broadband absorbing PA contrast agent based on semiconducting polymer nanoparticles (SPN-II) and apply it for PA imaging in NIR-II window. SPN-II can absorb in both NIR-I and NIR-II regions, providing the feasibility to directly compare PA imaging at 750 nm with that at 1064 nm. Because of the weaker background PA signals from biological tissues in NIR-II window, the signal-to-noise ratio (SNR) of SPN-II resulted PA images at 1064 nm can be 1.4-times higher than that at 750 nm when comparing at the imaging depth of 3 cm. The proof-of-concept application of NIR-II PA imaging is demonstrated in in vivo imaging of brain vasculature in living rats, which showed 1.5-times higher SNR as compared with NIR-I PA imaging. Our study not only introduces the first broadband absorbing organic contrast agent that is applicable for PA imaging in both NIR-I and NIR-II windows but also reveals the advantages of NIR-II over NIR-I in PA imaging.Keywords: brain imaging; photoacoustic imaging; Polymer nanoparticles; second near-infrared window;

Non-invasive monitoring of physiological signals during physical exercise is essential to customize the exercise module. Photoplethysmography (PPG) signal has often been used to non-invasively monitor heart-rate, respiratory rate, and blood-pressure among other physiological signals. Typically, PPG signal is acquired using pulse oximeter from finger-tip or wrist. Advantage of wrist-based PPG sensors is that it is more convenient to wear. Other sensors such as accelerometer can also be integrated with it due to large area on the wrist. This article provides a review of the algorithms developed for heart rate estimation during physical exercise from the PPG signals and accelerometer signals. The datasets used to develop these techniques are described. Algorithms for denoising of PPG signals using accelerometer signals are either in time domain or frequency domain.

•Resolution of an optical microscope is limited to 200 nm due to diffraction.•Photonic nanojet from a microsphere beaks the diffraction limit.•Microsphere was used for super-resolution imaging in optical imaging modalities.•Applications of microsphere in various microscopy imaging techniques are reviewed. The spatial resolution of a standard optical microscope (SOM) is limited by diffraction. In visible spectrum, SOM can provide ∼200nm resolution. To break the diffraction limit several approaches were developed including scanning near field microscopy, metamaterial super-lenses, nanoscale solid immersion lenses, super-oscillatory lenses, confocal fluorescence microscopy, techniques that exploit non-linear response of fluorophores like stimulated emission depletion microscopy, stochastic optical reconstruction microscopy, etc. Recently, photonic nanojet generated by a dielectric microsphere was used to break the diffraction limit. The microsphere-approach is simple, cost-effective and can be implemented under a standard microscope, hence it has gained enormous attention for super-resolution imaging. In this article, we briefly review the microsphere approach and its applications for super-resolution imaging in various optical imaging modalities.

Nanoparticles (NPs) with integrated functionalities of targeting, therapy, imaging contrast and biocompatibility have shown promise for application in improved disease diagnosis and therapy. Herein, we report a theranostic agent based on a narrow-bandgap small molecule, benzo[1,2-c;4,5-c′]bis[1,2,5]thiadiazole-4,7-bis(9,9-dioctyl-9H-fluoren-2-yl)thiophene (denoted as BBT-2FT), with the strong absorption of near-infrared (NIR) light. Colloidal nanoparticles composed of BBT-2FT showed a photoacoustic signal intensity ten times higher than that of blood, and high photothermal conversion efficiency (η = 40%) under the irradiation of 808 nm laser light, which killed over 90% of HeLa cells in 10 min.

Nanoparticles (NPs) with integrated functionalities of targeting, therapy, imaging contrast and biocompatibility have shown promise for application in improved disease diagnosis and therapy. Herein, we report a theranostic agent based on a narrow-bandgap small molecule, benzo[1,2-c;4,5-c′]bis[1,2,5]thiadiazole-4,7-bis(9,9-dioctyl-9H-fluoren-2-yl)thiophene (denoted as BBT-2FT), with the strong absorption of near-infrared (NIR) light. Colloidal nanoparticles composed of BBT-2FT showed a photoacoustic signal intensity ten times higher than that of blood, and high photothermal conversion efficiency (η = 40%) under the irradiation of 808 nm laser light, which killed over 90% of HeLa cells in 10 min.