Handheld Microfluidic Platform for Rapid Thrombin and SARS-CoV-2 Spike Protein Detection

Rapid detection of thrombin and SARS-CoV-2 spike protein is useful for very different clinical needs, from monitoring coagulation-related conditions to screening for viral antigens. However, many established assays require repeated washing, long processing times, trained personnel, and powered laboratory equipment. These limitations make it difficult to bring quantitative testing to decentralized or resource-limited settings. The challenge is therefore to create a microfluidic device that can detect both targets quickly, without complex sample preparation or an external pump.

Kwon and colleagues addressed this problem by developing a palm-sized microfluidic platform that combines a disposable microfluidic chip, a spring-driven handheld suction pump, aptamer-based gold nanoparticle sensing, and compact optical detection. Their platform was demonstrated for thrombin and SARS-CoV-2 spike protein by changing the target-specific aptamer. A built-in circuit processed the optical signal and transmitted the result by Bluetooth to a smartphone or computer, allowing real-time quantitative readout.

The detection mechanism is based on target-induced aggregation of gold nanoparticles. In the absence of thrombin or SARS-CoV-2 spike protein, the aptamers adsorb onto the nanoparticles and help keep them dispersed after salt is added. When one of the target proteins is present, its matching aptamer binds to the target instead of fully stabilizing the nanoparticle surface. Salt then promotes aggregation, shifting the solution from red toward purple and increasing the scattered light measured by the sensor. Because the optical signal develops directly from this interaction, the assay does not require washing or reagent exchange.

The microfluidic chip contained two inlet reservoirs, serpentine mixing microchannels, an optical viewing chamber, and a threaded outlet for connection to the pump. One inlet received the gold nanoparticles, aptamer, and target-containing sample. The second inlet received the salt solution. The upper section of the microfabricated chip was sealed using a transparent adhesive polyethylene film. The microchannels were 400 µm wide and 400 µm high, while the optical chamber held approximately 100 µL. The serpentine geometry was an important part of the system. As fluid moved through the curved microchannels, secondary Dean flows increased transverse mixing between the sample and salt streams. Compared with a straight microchannel, the serpentine design produced nearly twice the scattering signal, indicating faster and more uniform nanoparticle aggregation. Fluid transport was generated using a manually operated suction pump containing a plunger, compression spring, and two check valves. Pressing and releasing the button created negative pressure while preventing backflow. A single actuation produced approximately 24 kPa of negative pressure and filled the viewing chamber in about 20 seconds.

The microfluidic platform detected both thrombin and SARS-CoV-2 spike protein within about five minutes and produced concentration-dependent optical signals at sub-nanomolar levels in buffer. The handheld pump generated consistent pressure across different users, and the serpentine microchannel produced a stronger response than a straight microchannel under the same conditions. The researchers also tested thrombin in synthetic urine and SARS-CoV-2 spike protein in synthetic saliva. Although these sample matrices reduced or shifted the signal, both targets remained detectable.

Overall, the study shows how microfluidics, manual pumping, aptamer recognition, plasmonic sensing, and wireless electronics can be combined into one portable system. Its ability to detect thrombin and SARS-CoV-2 spike protein with the same basic workflow suggests that the platform could be adapted to other biomarkers by replacing the aptamer. Validation with patient-derived samples and further reduction of matrix interference will be important before the system can be used clinically.

 

Figures are reproduced from Kwon, DI., Yoo, YE., Jin, JH. et al. Microfluidic–optical integrated portable platform with handheld pump for wash-free plasmonic detection of thrombin and SARS-CoV-2 spike protein. Microsyst Nanoeng 12, 266 (2026). https://doi.org/10.1038/s41378-026-01381-3 under a Creative Commons Attribution 4.0 International License

Read the original article: Microfluidic–optical integrated portable platform with handheld pump for wash-free plasmonic detection of thrombin and SARS-CoV-2 spike protein

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