Provided is a obtaining an excitation-emission matrix, wherein the excitation-emission matrix is measured with a spectrometer by: illuminating a biological tissue with stimulant light at a first wavelength to cause a first fluorescent emission of light by the biological tissue, measuring a first set of intensities of the first fluorescent emission of light at a plurality of different respective emission wavelengths, illuminating the biological tissue with stimulant light at a second wavelength to cause a second fluorescent emission of light by the biological tissue, and measuring a second set of intensities of the second fluorescent emission of light at a plurality of different respective emission wavelengths； and inferring a classification of the biological tissue or a concentration of a substance in the biological tissue with a multi-layer neural network or other machine learning model.
