1.Overview

Today’s smartphones are essentially widely-used, powerful computers equipped with strong calculating capability, high-standard cameras, and online accessibility, which renders potent platforms for future portable biosensors and analytical devices. ^[1]
Based on this trend, this year we made a optical-based biosensors that can be operated with a smartphone.We named it "S.M.A.R.T."-S-Specific, M-Measurable, A-Accessibility, R-Relevant, T-Together. Effectual design combines the smartphone’s readily-accessible hardware and the optical and electrical components, allowing the device to take and measure accurate and precise fluorescence images of analytes loaded on microarray chips while remaining very portable. This combination also cleverly overcomes limitations, such as lighting conditions and camera positioning, as well as makes data available for cloud services.

2.Fabrication

The S.M.A.R.T. has a length of 186 mm, a width of 120 mm, a height of 92 mm and a mass of 2 kg. At the beginning of the design, we envisioned its functions and proposed key points.(Fig.1). It is divided into four modules, cradle, optical components, APP, electrical components. (Fig.2)

Fig.1: Workflow diagram

Fig.2: Instrument workflow diagram

2.1 Cradle Module

Fig.3: Solidwork design drawings

The material we choose is Resin 8000, which usually be used for 3D printing. It has good toughness and can adapt to ordinary assembly. And it’s heat distortion temperature is 46°, that means it is not easily deformed by heat.The drawing is shown in Fig.3.

2.2 Optical Components

It can reduce the impact of the environment on the test result, makes the environment controllable, and improve the repeatability of the test by placing the optical module inside the instrument.^[2]This module includes UV LED, yellow glass (equivalent to low pass filter), UV filter, support frame.(Fig.4)
We choose UV LED because it can stimulate red, yellow and green fluorescent proteins, which makes it easier to achieve high-throughput detection.On the other hand, the LED is small, low power, and environmentally friendly.
We use oblique light to excite the fluorescent protein, and the angle between the incident light and the normal is 45° so it can reduce the optical noise floor caused by the light from the bottom.

Fig.4 (a)UV LED,(b)yellow glass(equivalent to low pass filter,(c)UV filter

2.3 APP

In the high-tech era of high-speed development, smartphones are like a high-performance micro-multi-function processor. Therefore, when we are looking for more portable, higher-performance detection devices that make full use of the advantages of the Internet, we finally encountered this application——S.M.A.R.T. it’s an application that makes a mobile phone can control some main part of the device, and take the photo of the chip, and analyze the image.The icon we designed and software test results shown on Fig.6.
The mobile phone turns on the temperature control module through the S.M.A.R.T., after the device is activate，the temperature feedback will be displayed on the interface of S.M.A.R.T.
The device will keep operating according to the program set by the microcontroller, and the countdown of the device operations will be displayed on the application interface. After finished the operations, the LED will emit incident light, you just need to take a picture and S.M.A.R.T. will analyze the image. (Fig.7)

Fig.5 (a)S.M.A.R.T. icon(b)S.M.A.R.T. UI design(c) APP image analysis interface; (d) APP image capture interface.

Fig.6 The interaction between S.M.A.R.T. and the device

2.4 Electrical Components

The module includes: power supply module, microcomputer(MCU) and bluetooth. The power supply module is powered by a 5V DC power bank. The MCU we choose is MSP430-F5636 and the Bluetooth model is AB1602, BLE4.2. Power supply module provides a total voltage of 5V for MCU. The MCU controls the UV LED, temperature sensor, heating plate and Bluetooth through the clock. At the same time, Bluetooth provides data interaction between the App and the MCU. The workflow is shown in Fig.7.

Fig.7: Logic diagram of circuit design

3.Instrument Test

Our instrumentation has been carried from concept to physical. And we used the PMMA chip to do some exciting tests on our S.M.A.R.T.! Here are the results of our experiments!(Fig.8)(Fig.9)

Fig.8 This schematic providesa brief over the instrument's use.(a) Placing the mobile phone and the array chip to which the sample is to be placed on the respective mounting platform;(b)Inserting the chip into the instrument;(c)Turning on the LED lamp for detection.

Fig .9:The results of sodium fluorescein in the chip under different conditions (a) left to right in the left centrifuge tube: 0.01 MPBS buffer, 1 μM sodium fluorescein, 10 μM sodium fluorescein, 100 μM sodium fluorescein, right Chip to be tested; (b) chip inspection diagram under normal illumination; (c) chip inspection diagram under ultraviolet light conditions; (d) chip inspection diagram in S.M.A.R.T.

Reference:
[1]Roda A, Michelini E, Zangheri M, et al. Smartphone-based biosensors: A critical review and perspectives[J]. Trends in Analytical Chemistry, 2016, 79:317-325.
[2]Wang L J, Chang Y C, Sun R, et al. A multichannel smartphone optical biosensor for high-throughput point-of-care diagnostics[J]. Biosensors & Bioelectronics, 2017, 87:686-692.