Compact, rapid, and inexpensive smartphone-based point-of-care diagnostics is developing rapidly to replace conventional medical diagnostic procedures that necessitate specialized skills and bulky instruments. Smartphone-based biosensing protocols proposed to date involve “heterogenous” interactions of labels with functionalized sensing surfaces. In contrast, “homogenous” protocols do not require surface functionalization but are bulky and unsuitable for point-of-care diagnostics. In this work, we demonstrate a smartphone-based homogenous biosensing protocol that is portable, rapid, and low cost. Currents passed through microelectrode patterns fabricated onto silicon substrates produced dielectrophoretic forces that induced harmonic oscillations of 1-μm-diameter carboxyl-coated polystyrene particles suspended in aqueous solutions at well-defined heights above the surfaces of the chips. Next, we introduced 200-nm-diameter polystyrene particles functionalized with complementary amine compounds into the solution, which interacted with the larger particles, thereby significantly changing the oscillation dynamics of the larger beads. A smartphone was used to record the motion of the beads. Particle tracking and filtering algorithms were used to extract information about the oscillation of the particles and detect changes in their dynamics. The results showed that our approach enables the detection of the concentration of aminated particles with a smartphone within 1 min without requiring any prior functionalization of the biochip.