A low-cost, battery-powered PCR thermocycler with enhanced thermal stability for on-site detection of harmful cyanobacteria

• A low-cost (US$97), battery-powered portable PCR thermocycler was developed for field-deployable molecular detection. • The system integrates PID-controlled thermal regulation and efficient heat-transfer design, enabling stable ramp rates (+1.10 / –1.95°C/s) under portable operating conditions. • Custom mini-PCR tubes (30 μL) improve thermal transfer and reduce evaporation compared with conventional 100 μL tubes. • The device performs 30 PCR cycles in 78 min with amplification performance comparable to benchtop thermocyclers. • Successful amplification of 11 cyanobacterial genes demonstrates its applicability for rapid HAB monitoring and early-warning detection. Harmful algal blooms (HAB), intensified by climate change and eutrophication, pose severe risks to freshwater ecosystems and public health, particularly in communities relying on surface water as drinking sources. Effective HAB surveillance requires rapid and reliable molecular detection tools that can be deployed directly in the field, yet most existing methods for detecting dominant freshwater cyanobacteria remain laboratory-bound, lacking the portability and affordability needed for on-site use. Here, we introduce the point-of-care testing polymerase chain reaction (POCT-PCR) device, a handheld, battery-powered thermocycler (1.0 kg, US$97) designed for on-site DNA amplification. The system integrates an aluminum heat sink, dual ceramic heaters, a Peltier-based cooling module, and a fast-response thermistor all governed by Arduino-based PID control. Using custom mini-PCR tubes with a 30 μL capacity, substantially smaller than the conventional 100 μL PCR tubes, to enhance thermal transfer and significantly minimize evaporation, the POCT-PCR achieves ramp rates of +1.10°C/s and –1.95°C/s, enabling fast and stable thermal cycling (30 cycles in 78 min). Validation assays confirmed reliable amplification of eleven cyanobacterial genes, including those associated with toxin-producing strains, with reproducibility comparable to benchtop systems. Field validation further confirmed the device’s robustness and applicability under real environmental conditions. This low-cost platform enables rapid ecological surveillance and supports early-warning applications for harmful cyanobacterial blooms, expanding access to point-of-care molecular diagnostics for environmental and public health protection.