Magnetic Particle‐Based Thin‐Channel Analysis for Separation and Bioanalysis: From SPLITT Fractionation to Immunoassays

Magnetic particle‐based separation and analysis have become important tools in chemical and bioanalytical research because magnetic forces can be combined with particle surface chemistry, molecular recognition, confined‐flow transport, and diverse signal‐transduction strategies. This review discusses thin‐channel magnetic analytical methods as an interdisciplinary class of chemical analysis platforms that connect magnetic manipulation with separation science, microfluidic transport, and bioassay design. The emphasis is placed on split‐flow thin‐channel (SPLITT) fractionation, magnetic SPLITT, analytical magnetophoresis, magnetic deposition formats, and thin‐channel magnetic immunoassays. In these systems, thin, unpacked flow geometries shorten lateral transport distances and stabilize laminar trajectories, allowing modest magnetic forces to produce measurable particle displacement, outlet redistribution, deposition, capture, or signal enhancement. From a chemical perspective, the analytical performance of these methods depends on the coordinated design of magnetic‐field gradients, channel geometry, flow residence time, particle size and susceptibility, surface functionalization, matrix compatibility, and detector integration. This review summarizes the underlying principles, compares representative platform architectures, and evaluates how magnetic particles function as separation media, reactive interfaces, movable solid supports, and signal carriers. Particular attention is given to the transition from preparative magnetic separation to quantitative chemical and bioanalytical measurement. Remaining challenges include nonspecific adsorption, particle aggregation, field‐gradient control, calibration robustness, multiplexing, and translation to automated or portable devices. By framing thin‐channel magnetic analysis as a general chemical‐analysis strategy rather than a narrowly defined device format, this review highlights its relevance to analytical chemistry, bioanalysis, materials chemistry, and point‐of‐care diagnostic development.