Abstract: Microfluidic methods and systems for detecting levels of microorganisms via Mie forward light scattering. The systems and methods of the present invention can be customized so as to optionally maximize scatter from the particle immunoagglutination and minimize that of the sample matrix, e.g., via selection of parameters particle diameter d, wavelength of incident ?, and/or scatter angle ?. Methods feature providing beads conjugated with an antibody specific for the microorganism, mixing beads with a sample to form a first mixture; providing a control mixture; irradiating the mixtures with incident light; detecting forward light scattering scattered by the first mixture at a first angle with respect to the incident light and forward scattered light scattered by the control the same first angle with respect to the incident light; determining I and I0 from the light scattering; comparing I with I0; and determining a level of the microorganism.