Figure 7. Usability of mChip with naïve users.

(A) Usability rubric for running the mChip device showing number and percentage of participants who performed each step correctly. Slight modifications to the instructional video and app directions were introduced between the first and second set of participants (n=20 in each), with p-value calculations to show potential differences in performance. Two-proportion z-test was applied for p-value calculations. (B) Timing of test use showing a breakdown of time to completion, instructional video length, built-in timers and time of manual steps. (C) Participants’ self-evaluation of confidence in running the test correctly on a scale of 1–5 (not confident to very confident). (D) Comparison of positive control signals after channel priming. A 2μL plug of 0.05% Tween-PBS was flowed through the channel. At time points shown after channel priming, a 2μL sample of disease negative whole blood was introduced, followed by a standard reagent sequence for reconstitution of lyophilized gold-labeled anti-hIgG/anti-hIgM antibodies (three washes of 0.05% Tween-PBS, and four washes of water) and silver amplification. Data are averages ±1 SD (n=3). Asterisk (*) indicates statistical significance (p<0.05) using Student’s t-test. A comparison of signals at time point 0 and 2 hours after channel priming yielded minimal significance (p = 0.058). We observed a decreased signal in positive control zone signals with longer times between channel priming and running the assay. (E) Effect of lag time on fingerprick whole blood flow time through microfluidic channel. Condition 1 consisted of lag time measured in minutes between pricking the finger and subsequent collection and immediate introduction to the channel. Condition 2 consisted of collected the fingerpricked blood sample into the capillary tube of the sample collector, followed by lag time at indicated time points before introduction into microfluidic channel. Time for blood to flow through channel was measured in seconds from inlet to waste pad (end of channel). We saw that uninterrupted flow of the 2μL, unprocessed fingerprick blood sample sample to reach the waste pad, with channel priming was between 2– 2.5 minutes. 90% of participants took more than one minute between fingerprick blood collection and starting the assay (i.e. engaging the vacuum for fluid flow). (F) User activated negative pressure-driven flow showing average time to flow a total sequence of 4 washes: two-2uL washes of 0.05% Tween-PBS and two 2-uL washes of DI water, are shown. All three users were naive users (not enrolled in study, but unfamiliar with device). Data are averages ±1 SD (n=3). Asterisk (*) indicates significance, using one-way ANOVA followed by pair-wise t-test (P = 0.0248).