Quantification of samples is an integral step in numerous biological and chemical experiments. Spectrophotometers are often used together with colorimetric assays that react with the compound of interest in the samples. However, spectrophotometers are often costly, bulky and immobile. To increase the convenience and ease the process of spectrophotometry, the APD SpectBT was developed using the Arduino-based platform to create a smartphone dependent mobile spectrophotometer. Through a Bluetooth® connection, users can use a micro-USB portable spectrophotometer and send the readings to the smartphone app to get visible light absorbance readings conveniently. With the portable SpectBT device and app, users can easily perform spectrophotometry on the go in the field and immediate environments conveniently and rapidly.
The spectrophotometer is commonly used to quantify substances present in samples. When combined with colorimetric assays, the vis-spectrophotometer is a measures the absorbance of light by samples after passing a light beam through the liquid sample. A typical spectrophotometer consists of a light source, collimator, monochromator, wavelength selector, and photometer. Most important of these parts, are the spectrometer (used to produce desired wavelength of light) and photometer (used to detect absorption of photons).
Since its development, there have been numerous uses and functions that include the measurement of optical density (OD) of microbial cultures, quantification of biomolecules such as proteins using the Bradford assay (Bradford MM, 1976), nitrile/nitrate testing of water, NADH/NADPH enzyme assays, DNA and RNA quantification, and many others. By adjusting the wavelength of the light emitted and measured, the application of the spectrophotometer can be varied accordingly.
At present, current spectrophotometers are expensive (costing up to thousands of dollars) and bulky (requiring bench-top space). To improve the portability and cost, the APD vis-SpectBT was developed. This unique combination of both a portable spectrophotometer and the APD SpectBT App (used on a smartphone) takes away the need for costly equipment, large space area, and leverages on the smartphone. Increasingly, smartphones have been replacing equipments and bring about convenience (e.g. GelApp, See Sim et al., 2015; StanXY See Budianto et al., 2015) and have been increasingly leveraged on for the use of routine scientific and clinical uses (Gan SKE & Poon JK, 2016 & Gan SKE et al., 2016). As such, it is fitting for the development for a mobile spectrophotometer.
SpectBT is the combination of hardware and a smartphone app to allow users to effortlessly bring the spectrophotometer around for field research on-the-go.
The portable spectrophotometer measures 20 cm by 7.3 cm by 7 centimeters, and weighs 427 grams. Using light-weight acrylic and a sliding mechanism, cuvettes can be easily fitted. With 2-channels, the blank can be kept in for time-sensitive colorimetric assays. Boasting a rechargeable battery, the spectrophotometer can be charged using the highly common micro-USB port and offers hours of usage.
Figure 1: Top cross section of APD SpectBT spectrophotometer
A LED light passes through the selected filter lens (swappable based on the desired wavelength bands) and travels within the optical fibers and into the blank and sample cuvettes. Two silicon photodiodes are attached at the back of the cuvette holders to detect the light and convert them into absorbance in logarithms with a formula of 1V x log(blank/sample). The data is transmitted to the Arduino nano. The PCB circuit is designed and fabricated by EAGLE 7.7.
The acrylic casings protect the mechanical and electric parts and from the holding stations for the cuvettes, optical fibers and filter lens.
Comparing the APD SpectBT spectrophotometer with a commercial spectrophotometers (Nanophotometer X), using the same standards using bovine serum albumin in a Bradford Assay, we were able to show that device was able to function and give similar plots.
The limits of detection of both the Nanophotometer X and APD SpectBT were tested and were both found to have a linearity of a concentration of up to 3.75 mg/ml. Additionally, the APD SpectBT was demonstrated to have a 75.1% accuracy (see Table 1) and an R-squared value of 0.9407 (see Figure 2) when benchmarked against the bench top spectrophotometer.
Table 1: Comparison of commercial Nanophotometer X and APD SpectBT Spectrophotometer
Figure 2: Plotted Standard Curve. Commercial Nanophotometer X is shown in blue while APD SpectBT Spectrophotometer is shown in red.
The APD SpectBT App allows users to connect the SpectBT device to their smartphones via Bluetooth without any internet connectivity.
By pairing via Bluetooth, users can control and receive readings from the device (see Figure 4). To keep the device small, all controls such as the light source are performed through the app. The devices does not have memory since all readings are taken and saved on the smartphone by the app. The tabulated results can be edited, deleted, and exported (as .CSV file) to the app folder in Android.
Figure 3: Interface of the APD SpectBT App.
The file can then be emailed or synced to cloud apps (e.g. Dropbox, Google Drive, etc) for desktop plotting of graphs or other mobile apps (e.g. StanXY App, see Budianto et al., 2015) for further analysis and the quantifying unknown samples.
C++ programming is used in Arduino’s system by ARDUINO 1.6.13 to enable Bluetooth communication. Information sent from the smartphone to the Arduino system will be interpreted before executing a certain task e.g. control of light.
The APD SpecBT App for Android was developed using version 4.2 of the Eclipse Integrated Development Environment, Juno.
APD SpectBT was specifically designed to be portable and can be used both in and outside laboratory settings.
Common laboratory applications include the measurement of the optical density (OD) of a bacterial culture and quantify protein concentration. Alternatively, when coupled with colorimetric assays e.g. Bradford protein assay (Bradford MM, 1976), the concentration of protein in unknown samples can be performed. By simply swapping the light band filter at the filter holder, SpectBT can be adapted to suit a wider range applications. By switching to a UV light source, biomolecules can also be utilized.
As many applications, in particular biological samples, can degrade when not in proper storage, the use of SpectBT for field research is highly valuable. The portability and internet-independent use also makes is suitable for rural or inaccessible areas, improving the accuracy of results by fresh sampling.>
APD SpectBT is a smartphone-dependent portable spectrophotometer that brings convenience and efficiency to absorbance measurement. With a micro-USB chargeable in-built battery and customizable light-source and band filters, users can now accurately measure absorbance of their samples in the field in a wide range of applications conveniently and on-the-go.
The APD SpectBT App is developed for Android and is freely available on the Google Play Store. More details on the app can be found at www.facebook.com/APDLab The APD SpectBT user guide is available at http://tinyurl.com/SpectBT, linked in the ‘About Us’ page of the app. A video tutorial is also available on the Google Play Store or http://tinyurl.com/SpectBTvideo
This work is self-funded by the authors.
Bradford MM (1976) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Analytical biochemistry, 72(1-2), pp.248-254.
Sim JZ, Nguyen PV, Lee HK, Gan SKE. GelApp: Mobile gel electrophoresis analyzer. Nature Methods Application Notes. doi: 10.1038/an9643
Gan SKE, Poon JK (2016) The World of Biomedical Apps: their uses, limitations, and potential. Scientific Phone Apps and Mobile Devices. Vol 3 (Accepted). Corresponding author.
Gan SKE, Koshy C, Nguyen PV, Haw YX (2016) An Overview of clinically and healthcare related apps in Google and Apple app stores: connecting patients, drugs, and clinicians. Scientific Phone Apps and Mobile Devices. Vol 3
Budianto, I.H., Wong, C.F., Nguyen, P.V. and Gan, S.K.E., 2015. StanXY: standard curve app for Android. Scientific Phone Apps and Mobile Devices, 1(1), p.1.