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Wireless fluorimeter for mobile chemical sensing

Wireless chemical sensors are devices which can collect data about their local (bio)chemical environment, or perform spot-tests on applied samples, and then process and transmit this chemical analytical information to a remote device by wireless technology (see Fig1). Wireless data transfer offers several advantages over wired systems, such as improved mobility, unobtrusiveness and lower installation costs. This is especially advantageous in applications where chemical analytes need to be monitored long-term in-situ or in inaccessible places [1]. In this work a wireless chemical sensor for fluorescence intensity measurements has been developed (Fig2). It is based on Radio-Frequency Identification (RFID), and can wirelessly transmit collected data to an RFID reader or to a Smartphone by near-field communication (NFC) technology. It can operate in both ad-hoc query mode and as a datalogger, capable of storing up to 32 000 data points. The optoelectronic components are integrated on the tag: an LED source is used to excite the fluorophore and a photodiode which collects the fluorescence light is positioned at a 90° angle. The emitters and detectors can be changed at will depending on the application and fluorescent dye used. Operation of the wireless fluorimeter has been evaluated in a proof-of-concept experiment where different concentrations of fluorescein in water have been detected. Fluorescein is a commonly used luminescence standard with a large quantum yield, and was selected here as a model analyte. It has an excitation maximum at 494 nm, so a cyan LED with a peak wavelength at 502 nm was used for excitation (Fig3). The excitation light is filtered out by placing a bandpass optical filter between the fluorescein solution and the photodiode, so only fluorescence is detected by the photodiode. The photodiode signal is then wirelessly transmitted to a nearby reader, and the data is analysed. When fluorescein concentration is increased there is an increase in fluorescence intensity detected by the photodiode (Fig4). This response is linear in the concentration range 10-4 to 10-6 M (R2 = 0.9961). First experimental results demonstrate the functionality of the system. Further investigation into the analytical performance of the RFID fluorescence sensor is required. The system can be further optimized by using different optoelectronic components (such as wavelength- specific photodiodes or high-intensity LEDs) or different geometric arrangements. Wireless chemical sensors such as the one presented here could make a large contribution to emerging fields of research, such as wearable sensors in healthcare and sport activities, wound monitoring and point-of-care diagnostics [2, 3].

Wireless chemical sensor; Fluorescence sensors; Radio-frequency identification

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