The speed of data acquisition is a major hurdle for hyperspectral spontaneous Raman imaging to be widely adopted in the clinical setting. To address this problem, we proposed a new approach to achieve fast spectroscopic imaging while keeping high spectral resolution, in which narrow-band or wide-band imaging quickly captures all required data and then full spectra at all pixels are reconstructed efficiently. We started by developing a method to enable the reconstruction of diffuse reflectance spectra from color images with high accuracy. This method was further developed for hyperspectral Raman imaging from narrow-band measurements. Then a series of Wiener estimation based methods were developed to improve the accuracy of spectral reconstruction and reduce the need of acquiring a training dataset. A four-channel Raman imaging system has been built to acquire all narrow-band images in one single frame and an eight-channel imaging system is currently under evaluation. This technique could speed up the acquisition of hyperspectral data cube by two to three orders of magnitude, which opens the possibility of rapid Raman imaging for the monitoring of dynamically changing events in biological samples. Moreover, other hyperspectral imaging modalities including diffuse reflectance and fluorescence imaging can also benefit from this fast spectroscopic imaging technique, which have been demonstrated in flap assessment during plastic surgery on an animal model.
In this work, we report a novel substrate for surface enhanced Raman spectroscopy (SERS) composed of silver nanoparticles protected by small nitrogen-doped Graphene Quantum Dots, i.e. Ag NPs-N-GQDs, synthesized under mild experimental conditions, which can preserve the SERS performance in normal indoor environment for up to 30 days. The field emission scanning electronic microscope (FESEM) images confirm that the N-GQDs play a significant role in the control of metallic nanoparticles morphology. The X-ray photoelectron spectroscopy (XPS) result clearly indicates the N-GQDs was successfully immobilized on the surface of silver nanoparticles (Ag NPs). Ag NPs-N-GQDs demonstrated Raman enhancement stronger than pure Ag NPs likely due to an increase in the number of the “hotspots” formed by coupled nanostructures. N-GQD protected Ag NPs were evaluated in SERS measurements of R6G when they were made fresh and have been stored in normal indoors condition for up to 30 days. Then Ag NPs-N-GQDs were used as a SERS substrate for glucose detection. The linearity range of glucose was found to be ranged from 1 μM to 1 M with a detection limit of 0.1 μM in glucose solutions. It was also applied successfully for glucose detection in rat blood samples. The present study demonstrates that the novel Ag NPs−N-GQDs nanostructure has great potential to be used as a cost effective sustained SERS substrate, which can be extremely useful in the wide adoption of SERS based sensors.
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