Progressing Microfluidic Chips for Separating Sperm from Mixed Stain of Seminal and Vaginal Substances

The mixed stain of seminal and vaginal substances is significant evidence commonly found in sexual assault cases. How to isolate the involved perpetrator’s sperm and obtain its STR profiles is always the key to solving the relevant issue and the task any forensic DNA laboratory has to tackle. Many techniques have been invented to deal with the mixed stain, but the mainstream choice presently used in domestic laboratories is the differential lysis or its modified version. Although the methods mentioned above are of simple principle and low cost, they have still tended to bear some disadvantages that are difficult to overcome, e.g., long time-consuming, many processing steps, complex operation, low degree of automation, and difficulty in getting a single male STR genotyping in the case of entanglement with many female components. Microfluidic chips, an ever-developing technology based on different principles, have been innovated and used for capturing sperm in forensic cases. Compared with the traditional methods, microfluidic chips assume their advantages as the following rough aspects: less sample consumption; rapid high-throughput extraction, greater portability, great integrative and automotive potential; increased concentration and purity of isolated spermatozoa in the final product. Currently, there are five different types of microfluidic chips applied for separating sperm from the mixed stain of seminal and vaginal substances: one relying on different sediment velocities and adherence properties that utilize hydrodynamic filtration and pinched flow fractionation, one taking acoustic differential extraction, one basing on dielectrophoresis, and the SLeX-carbohydrate microarrays. Microfluidic chips were summarized here based on the difference in the involved two cells’ physical characteristics and ligand-specific combination according to separation mechanism, with an overview being carried out about the development of each type of microfluidic chips-the technical principle, latest progress, advantages and disadvantages, coming-up research direction, and lastly a brief comparison among the chips discussed. The continuous improvement of related technologies will be definite to launch such microfluidic chips of small size, fast response, and stable output effect that are potentially widely applied for various levels of forensic DNA laboratories to dispose mixed stains from cases.