Fig 1.
Experimental setup rendered in exploded and assembled view.
The setup (A-B) contained a microfluidic chip with 2 microreactor cavities holding 0.1 ml liquid volume in total, and an integrated self-regulating microheating element (Heatron Inc. BM117-83) attached to a carrier (D). Fluidic inputs were connected to 3 ml syringes. The fully assembled setup for thermal characterization (C) was connected to 2xAAA batteries to power the heating element, and a temperature probe was fixed for temperature recording with thermoplastic adhesive in one of the reactor cavities.
Table 1.
Design parameters for self-regulating PTC polymer heaters from Heatron Inc.
Table 2.
Boundary conditions and initial parameter values for the model.
Table 3.
Material properties for the model.
Table 4.
A summary of samples of BM117-83 batch self-regulating resistive heating elements.
Fig 2.
Heating element sample performance in the tested Lab-on-a-Chip experimental setup.
Although differences were minor, heating element BM117-83-B1 was the most suitable candidate from the tested samples, both with respect to steady-state temperature and rise times achieved during the test.
Fig 3.
Comparison of the simulated temperature distribution to the thermal image of the physical prototype.
Both simulated (A) and experimentally recorded (C) images are shown in steady state. Heating element BM117-83-B1 was selected as the candidate for comparison due to its favorable performance. Its temperature-dependent resistivity profile was fed into the model. In both the physical and simulated prototype, temperature probes were placed in the same spot (see Fig 1C) and recorded steady-state temperatures compared. The model estimated recorded temperatures with less than 0.2°C absolute error.
Fig 4.
Color maps showing the spatial distribution of temperatures in the microreactor cavity.
The temperature distribution map (A) indicated a gradient from the inner towards the outer reactor wall, however, the cross-section (cut plane marked in green) indicated that the microreactor temperature was within the specified target range of 60–63°C (B). Calculations based on model outputs indicated that ≈85% of the reaction volume was within the target range in steady state (C).
Fig 5.
Evaluation of the self-regulating resistive heating element with an on-chip isothermal nucleic acid amplification protocol.
Two Lab-on-a-Chip prototypes with two reaction chambers were prepared along with reaction volumes including samples and master mix separately (A). After 30 minutes of incubation with the heating element, reaction volumes were extracted into Eppendorf tubes and lateral flow strips were added to detect amplicons. The experiment was repeated twice with two chips. Results indicated a successful amplification for all 8 reaction volumes (B). The result was confirmed by separately performing LAMP for a positive and negative control in Eppendorf tubes (C).