A mobile phone-based dark field microscope (MDFM) apparatus suitable for quantifying nanoparticle signals is provided. The MDFM apparatus includes an electrically operated light source, a dark-field condenser, a slide housing configured to receive an analytical slide, and an adapter housing configured to receive an objective lens and receive a portable electronic communication device. The slide housing positions the analytical slide between the objective lens and the dark-field condenser. The adapter housing registers the objective lens with a camera lens of the portable electronic communication device. A method for performing a biological quantitative study using the dark-field microscope apparatus is further provided.