# Multi-mode Microscopic Hyperspectral Imager for the Sensing of Biological Samples
## 4 Discussion  
We developed a multi-mode microscopic hyperspectral imager (MMHI) for the sensing of biological samples. The coaxial structure of illumination and detection ensures a uniformly-illuminated condition in FOV, so that possible shadows in the focal plane can be obviated. The spatial and spectral resolutions are 5 \(\upmu\)m and 3 nm, respectively, to meet the microscopic observation for most biological samples. By replacing the objective with a higher magnification or the slit with narrower width,  
Figure 5: (**a**) Measured fluorescence spectra of five disaster-causing microalgae by the multi-mode microscopic hyperspectral imager (MMHI) system. (**b**) Normalized spectra of (**a**) through Equation (3). (**c**) Measured fluorescence spectra of five disaster-causing microalgae by a commercial spectrometer. (**d**) Normalized spectra of (**c**).  
Figure 6: Classification with the experimental data for five disaster-causing algae samples. (**a**) The relationship between principal component (PC)1 and PC2. (**b**) The relationship among PC1, PC2 and PC3.  
the spatial or spectral resolution can be further improved. Since the system adopts a push-broom scan mode, a large imaging region can be achieved for various application scenarios.  
Three experimental detections in Section 3 demonstrated the capacity of our MMHI system in the transmission, reflection and fluorescence modes, providing potential areas of application, such as zooplankton detection [4], biometric applications [24; 25] and environmental monitoring [26]. These experiments also show the feasibility of the MMHI system to detect samples with different characteristics, such as the transmission mode for transparent/translucent samples, the reflection mode for opaque samples and the fluorescence mode for fluorescent samples. We may additionally combine the results under different detection modes with artificial intelligence, e.g., the supervised learning algorithm [20], to achieve the feature extraction of a specific sample from a complex environment. If the captured images are written into the CMOS camera memory directly rather than a computer hard disk, a scanning rate of 1000 frames per second can be expected, which will greatly improve the applicable ability in on-site scenarios.  
In terms of future improvements, higher speed of imaging, wider range of detected wavelength and multi-dimensional detection should be considered. The staring imaging mode through a galvanometer mirror can largely improve the scanning as well as imaging efficiency, providing a low-cost solution for fast measurement. Additionally, by designing optical structure and selecting special components, the wavelength band of the MMHI can be expanded to near-IR band for in-vivo detection [27]. Furthermore, combining the hyperspectral imaging technology with 3D microscopic inspection methods [28], the 2D hyperspectral image may be extended to 3D hyperspectral topography. We believe that the MMHI will have more applications in multi-functional bio detections in the future.  
[PERSON] designed/modified the experimental optical path and instrument, [PERSON] and [PERSON] performed the experiments and analyzed the data, [PERSON] and [PERSON] wrote this manuscript. [PERSON] supervised the work and finalized the manuscript. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Key Research and Development Program of China (No. 2018 YFC1407503), the Fundamental Research Funds for the Central Universities (Zhejiang University NGICS Platform), the National Natural Science Foundation of China (11621101), and the Science and Technology Development Plan Project of Changshu (No.CS201806). The authors are grateful to [PERSON], [PERSON], [PERSON] and [PERSON] for valuable discussion and help. The authors declare no conflict of interest.