High-resolution optical longitudinal cortical imaging usually uses cranial window, which involves removing a skull portion and sealing the exposed brain area with a transparent cover glass, allowing ballistic photons to reach the cortex with minimal disturbance of the brain function. It enables obtaining high-resolution brain images in extended periods of time for long-term neuronal activity studies using confocal and two-photon microscopies. Photoacoustic microscopy (PAM), as the only imaging method that directly measure absorption contrast, is a complementary functional imaging method to provide absorption related brain information, such as total concentration of hemoglobin and oxygen saturation of hemoglobin. However, the use of traditional piezoelectric transducers (PZT) to collect ultrasound signal greatly limits the versatility of PAM. Though highly sensitive, PZT transducers are usually bulky and optically opaque. It blocks the light and is hard to be inserted into the limited distance between the optical objective and imaging sample, which are normally less than one millimeter when using a high- numerical aperture (NA) objective to achieve submicron resolution.
Here, we developed a simple and cost-efficient soft nanoimprint lithography (NIL) process to fabricate fully embedded micro-ring resonator ultrasound detectors on optically transparent substrates, and integrated the detector onto a cranial window, making cranial window itself an ultrasonic detector. We implanted this functional cranial window on mouse head and achieved longitudinal monitoring of cortex vasculature using PAM. Our low-cost, disposable, and optically transparent detector may potentially reshape the longitudinal functional brain imaging using PAM in small animals.
Optical fiber provides a unique and versatile platform for developing point-of-care optical sensing systems. Here we first
propose a Fabry-Pérot (FP) based flow-through optofluidic biosensor, and then construct an all-fiber system which fully
utilizes optical fibers to achieve rapid, sensitive, label-free biomolecular detection. This sensor consists of two single
mode fibers (SMFs) with reflecting surfaces and a photonic crystal fiber (PCF) vertically sandwiched by them. Firstly,
the SMFs act as waveguides for delivering light into and out of an optofluidic device (like PCF); secondly, instead of
using the optical properties of the PCF, we take advantage of its inherent multiple fluidic channels and large sensing
surface; thirdly, the two reflective surfaces and the PCF form a Fabry-Pérot microresonator and its resonance mode is
sensitive to the change in the fluidic channels, which can be used to detect the substances flowing through the fluidic
channels or adsorbing on the channel surface. In this paper, we explore the operating principle of the FP-based
optofluidic biosensor, theoretically and experimentally investigate its feasibility and capability. The results show that the
all-fiber optofluidic sensor is a promising technology platform for rapid, sensitive and high-throughput biological and
chemical sensing.
We report that by using a single mode coupled microcavity laser, we successfully realized a sensitivity of 80 pg/ml for
detecting BSA. The detecting scheme also works for other bio samples. The result proves that active sensing with
microcavity laser can achieve ultrahigh sensitivity. Further analysis shows that the ultra-sensitivity comes from the slight
change of coupling coefficient between the two coupled microcavities.
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