This pervasiveness, as well as the increasing computational ability of smartphones, makes them an ideal mobile platform for collection and analysis of (bio)chemical data ( Zhang and Liu 2016). According to the International Telecommunication Union (ITU), mobile cellular subscriptions reached 7.4 billion globally in 2016, almost reaching the number of people on Earth ( ITU 2016). One mobile platform particularly being increasingly used in (bio)chemical sensing РІР‚вЂњ the smartphone РІР‚вЂњ has now become ubiquitous. Thus, both radio and visual readout systems are receiving attention from the academic community. However, in a wearable optical system, the output signal can also be read by the naked eye or a camera ( Figure 1B).

Wireless (radio-based) communication is often essential to ensure complete mobility of many types of wearable sensor, especially electrochemical devices ( Steinberg, Kassal, and Steinberg 2016). Several review papers have been published on electrochemical wearable sensors ( Windmiller and Wang 2013, Bandodkar and Wang 2014, Steinberg, Kassal, and Steinberg 2016, and Malon Radha, Heng Lee, and CР“С–rcoles Emma 2017), but no similar review has yet been undertaken on optical wearable sensors. 2008) and has been the research focus of analytical chemists for many years. Wearable chemical sensing is becoming a key application area for wireless chemical sensors ( Diamond etРІР‚вЂ°al. (B) Mobile optical sensors also enable wireless readout by the naked eye or a remote camera, without radio communication. (A) Schematic showing the operation of a wireless optical (bio)chemical sensor. In a radio-based wireless optical chemical sensor, the optical signal generated by the interaction of the analyte and receptor chemistry is converted to an electrical signal by the detector and is then passed to a remote wireless receiver or network where the data can be analysed in more detail ( Figure 1A). Optical chemical sensors and biosensors lend themselves to integration into wireless systems thanks to their ease of miniaturisation, the unnecessary use of reference electrodes, the high detection sensitivity of certain modes (e.g., fluorescence), and the diversity of optically responsive indicator chemistries. Common radio technologies used in such systems include Bluetooth, radiofrequency identification (RFID), ZigBee, near field communication (NFC), and 433- and 860-MHz short-range devices (ISM/SRD860) ( Kassal, Steinberg, and Steinberg 2018). These hybrid sensing devices collect analytical data on their local (bio)chemical environment, or perform spot tests on applied samples, and process and transmit this information to a remote device wirelessly, most usually by radio communications ( Farre etРІР‚вЂ°al. The demand for instant (bio)chemical information at the point of measurement combined with advances in mobile communication technologies is driving the development of wireless chemical sensors and biosensors for the sensor Internet of Things.

We conclude that despite the challenges, mobile and wearable optical chemical sensor systems are set to play a major role in the sensor Internet of Things. In particular, the current trend for personal fitness tracking is driving research into novel colourimetric wearable sensors with smartphone readout.

The analysis of 77 original research articles published between 20 reveals that healthcare and medicine, environmental monitoring, food quality, and sport and fitness are the target markets for wireless and mobile optical chemical sensor systems. In each section, the specific challenges and trade-offs surrounding the (bio)chemical sensing mechanism and material architecture, miniaturisation, integration, power requirements, readout, and sensitivity are explored with detailed examples of sensor systems from the literature. The review is organised into three sections, each of which investigates a major class of wireless and/or mobile optical chemical sensor: (i) optical sensors integrated with a radio transmitter/transceiver, (ii) wearable optical sensors, and (iii) smartphone camera-based sensors. This review explores the current state-of-the-art wireless and mobile optical chemical sensors and biosensors.

Oxygen forensics 20154