A smartphone is optically coupled to an apparatus that can operate in multiple modes to perform transmission, reflectance, intensity, or scattered light spectroscopy on a sample provided, in an appropriately configured sample cartridge. The apparatus includes a first illumination optical path for illuminating the sample, with light from a light source, on the smartphone for transmission, reflectance, and scattered light spectroscopy. The apparatus also includes a second illumination optical path for illuminating the sample with light from a laser diode for intensity spectroscopy. The apparatus farther includes a collection optical path for collecting light from the sample in each of the modes. An image sensor on the smartphone receives the collected light via a diffraction grating to obtain a spectrum image. The first illumination optical path is substantially parallel to the collection optical path, whereas the second illumination optical path is substantially orthogonal to the collection path.