A new approach to direct quantitative detection of small molecules (haptens) by dynamic light scattering biosensing is presented. The proposed technique implements a homogeneous competitive immunoassay and is based on optical detection of specific inhibition of nanoparticle aggregation induced by the analyte in a sample. The technique performance was tested both in buffer and milk for detection of chloramphenicol - antibiotic relevant to food safety diagnostics. Good specificity, sensitivity (LOD in milk is 2.4 ng/ml), precision (4.0 ± 1.2%), ruggedness (8.3%), and 96% recovery in conjunction with a record wide dynamic range (3 orders of magnitude) of the nanosensing technique were demonstrated. Such characteristics complemented by the assay simplicity (no washing step) and a short assay time make the approach attractive for application as an analytical platform for point-of-care and field-oriented diagnostics. Graphical abstract.
Keywords: Chloramphenicol; Gold nanoparticles; Homogeneous assay; Magnetic nanoparticles; Optical biosensor.