Additively manufactured electrothermal thin-film heaters for on-chip isothermal DNA amplification

Abstract

Reliable thin-film heaters that provide rapid and uniform heating are critical for point-of-care molecular diagnostics. In this work, we present the additive manufacturing of electrothermal thin-film heaters that are directly integrated with an on-chip chamber. This configuration enables isothermal amplification of deoxyribonucleic acid (DNA) in a portable and compact platform. Two additive processes were compared. The first was a five-layer inkjet-printed (5L-I) heater, optimized using a 10 min oxygen plasma treatment and a 40 degrees C substrate (0.5 % uncoverage at five layers). The second was a single-layer direct ink writing (DIW) printed heater (1L-D) with conformal coverage. Infrared (IR) thermography showed quadratic voltage-temperature scaling for both heaters. The 1L-D heater achieved similar to 1.7 times higher maximum temperature and faster heating/cooling rates, consistent with lower resistance and higher conductivity. Long-duration thermal assessments confirmed that the 1L-D heaters sustained stable temperatures over 60 min (79.5-81.9 degrees C at 3 V; CV < 1 %), demonstrating high reproducibility and reliable performance for continuous isothermal operation. Under water-filled chamber conditions, the 1L-D heater maintained uniform in-plane temperatures (59.3-62.5 degrees C at 3 V; CV < 1.02 %), outperforming the 5L-I heater (CV approximate to 3 %). Parallel Loop-mediated isothermal amplifications (LAMP) at 65 degrees C for 30 min were performed using both the on-chip chamber and a benchtop thermocycler. These tests produced comparable colorimetric and gel electrophoresis results for the target plasmid DNA, pNL1.2, with little amplification observed for the non-target control plasmid, pPZP-RCS2. Overall, the DIW heater provides rapid, uniform, and stable heating suitable for reliable point-of-care isothermal amplification.