Disclosed are methods, systems, and devices for detecting biological analytes in a sample. The disclosed technology can be used to obtain readings of analyte concentration in a sample by imaging scattered light from an angled narrow beam illuminator. A fluid sample containing one or more biological, organic, and inorganic analytes including proteins, viruses, bacteria, phages, toxins, peptides, DNA, RNA, hormones, chemicals, drugs, and isotopes can be transferred to a microfluidic device having one or more channels with dimensions to generate capillary action for sample transport. The geometry of the microfluidic device may include a reservoir and sensing area, wherein an immunometric reaction can take place for the narrow beam scanning. The test particle may be coated with a specific binding member that is used to bind the binding pair member on an analyte in a sample. Test particles form the binding and the particle/analyte conjugate may be scanned.