Smart Cup: A Minimally-Instrumented, Smartphone-Based Point-of-Care Molecular Diagnostic Device

Abstract

Nucleic acid amplification-based diagnostics offer rapid, sensitive, and specific means for detecting and monitoring the progression of infectious diseases. However, this method typically requires extensive sample preparation, expensive instruments, and trained personnel. All of which hinder its use in resource-limited settings, where many infectious diseases are endemic. Here, we report on a simple, inexpensive, minimally-instrumented, smart cup platform for rapid, quantitative molecular diagnostics of pathogens at the point of care. Our smart cup takes advantage of water-triggered, exothermic chemical reaction to supply heat for the nucleic acid-based, isothermal amplification. The amplification temperature is regulated with a phase-change material (PCM). The PCM maintains the amplification reactor at a constant temperature, typically, 60-65°C, when ambient temperatures range from 12 to 35°C. To eliminate the need for an optical detector and minimize cost, we use the smartphone's flashlight to excite the fluorescent dye and the phone camera to record real-time fluorescence emission during the amplification process. The smartphone can concurrently monitor multiple amplification reactors and analyze the recorded data. Our smart cup's utility was demonstrated by amplifying and quantifying herpes simplex virus type 2 (HSV-2) with LAMP assay in our custom-made microfluidic diagnostic chip. We have consistently detected as few as 100 copies of HSV-2 viral DNA per sample. Our system does not require any lab facilities and is suitable for use at home, in the field, and in the clinic, as well as in resource-poor settings, where access to sophisticated laboratories is impractical, unaffordable, or nonexistent.

Keywords: Chemical heating; HSV-2 virus detection; Loop mediated isothermal amplification; Smartphone; microfluidics.

Fig. 1

(A) Exploded view of smart cup for minimally-instrumented, point-of-care molecular diagnostics. The smart cup consists of a thermos cup body, a 3D-printed cup lid, a chip holder, and a smartphone adapter. Inset is a photograph of Mg-Fe alloy pouch ($ 0.15 per pouch) used as a heating source. (B) A photograph of a fully assembled, smart cup equipped with a Samsung Galaxy S3 smartphone. Inset is a photograph of an integrated microfluidic chip containing three independent, multifunctional, isothermal amplification reactors for nucleic acid extraction and amplification.

Fig. 2

(A) The amplification reactor’s temperature as a function of time when the ambient temperature varied between 12 °C to 35 °C. (B) A thermograph of the heated surface of the microfluidic chip holder taken with an infrared camera (T360). The three reactors of the microfluidic chip are located within the dashed square.

Fig. 3

(A) Real-time monitoring of LAMP amplification of transport media samples spiked with 420 PFU per sample (curve 1), 42 PFU per sample (curve 2), 4.2 PFU per sample (curve 3), and 0 PFU per sample (curve 4) (negative control). (B) The threshold time Tt (in minutes) is depicted as a function of the HSV-2 concentration (expressed in terms of PFU per sample) (n = 3).