Naslov
Sol-gel thin films as (bio)chemically responsive layers in integrated optoelectronic wireless sensors

Autori
Sabljić, Petra ; Šnévajsová, Petra, Steinberg, Matthew D. ; Murković Steinberg, Ivana

Vrsta, podvrsta i kategorija rada
Radovi u zbornicima skupova, cjeloviti rad (in extenso), znanstveni

Skup
YISAC 2008 (Young Investigators Seminar on Analytical Chemistry)

Mjesto i datum
Ljubljana, Slovenija, 02.04.2008

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
optical wireless sensors; urease immobilisation;

Sažetak
Sol-gel glasses have been widely used as solid matrices for immobilisation of chemical and biochemical reagents used in chemical sensors and biosensors, particularly in optical sensors [1]. Sol-gel technology is especially convenient for development of optical sensors since it allows low-temperature preparation of optically transparent porous thin films with tunable properties. In addition, preparation of sol-gel sensing layers in a form of thin films using spin-coating offers a simple and reproducible deposition method. Processability of sol-gel thin films using standard deposition methods as well as their versatility as immobilisation matrices for different reagents including biomolecules such as proteins, enzymes and antibodies, makes them ideal candidates for development of chemically sensitive layers in integrated chemical sensors and biosensors. Especially attractive is the possibility of using sol-gel thin films as a part of planar waveguides in integrated optoelectronic sensing devices. A new generation of chemical sensors and biosensors is emerging as a result of the integration of chemical and biosensor technologies with wireless devices, and has particularly attractive potential applications in healthcare, personal care, environmental monitoring, process and quality control, and chemical and biological threat detection [2]. We have developed an OptiTag as a wireless chemical sensor platform based on the ISO standard radio-frequency identification (RFID) protocol, shown in Figure 1. OptiTag is the fusion of an optoelectronic detector with an RFID processor into a credit-card sized device and has potential application as a chemical sensor node in a wireless sensor network (WSN). Fig. 1 OptiTag with LEDs and a photodiode, and the development electronic board The objective of the work presented here is to develop and integrate an optical chemical sensor and optoelectronic interface onto a wireless RFID tag and to demonstrate its function via optical determination of pH and urea as model analytes. For this purpose, pH sensitive thin-films were made on glass substrates by spin-coating a cocktail of the colour indicator dye bromocresol green (BCG) together with a sol-gel precursor and surfactant. Immobilised bromocresol green (BCG) indicator dye reversibly changes colour in the visible region of the spectrum from pale yellow at pH 4 (protonated state) to dark blue at pH 8 (de-protonated state) with the response in the range of seconds or less. The absorbtion spectrum has an isosbestic point at a wavelength of 505 nm and a strong absorbtion peak at 615 nm which increases with pH. Coated glass chips were placed onto the optoelectronic interface of the OptiTag consisting of a pair of light emitting diodes (LEDs) operating at wavelengths of 505 nm (cyan, λ iso) and 617 nm (red-orange, λ sig). They are used to sequentially illuminate the pH sensitive BCG thin-films and the transmission of light through the film at both wavelengths is determined with the photodiode before and after exposure to buffer solutions of different pH values. Next, urea sensitive sol-gel thin films were developed by immobilising urease enzyme. The sensing scheme is based on the enzymatic degradation of urea which generates OH- ions causing an increase in pH value, which may be monitored using the pH sensor described above. For this application, urease was immobilised in sol-gel thin films using different thin film configurations (single-layer or multi-layer configurations). Optimisation of the sol-gel cocktail composition and the spin-coating processing parameters for different film thicknesses, were peformed. Also, the effects of different pH buffers on enzyme activity were studed and the results are presented. It has been demonstrated that by adapting and modifying the specific chemistry and optoelectronic detector measurement strategy, the OptiTag platform could be deployed in various chemical and biological sensing applications. Such applications might in the future include wearable sensors for chemical and biological exposure and contamination monitoring, environmental monitoring, and long-term in-situ monitoring as embedded sensors. The research presented here is supported by Erasmus Technology LLP, UK, the National Foundation for Science, Higher Education and Technological Development of the Republic of Croatia (NZZ), and the MZOS RH (grant number: 125-0000000-3221). [1]Jerónimo, P. C. A, Araújo, A. N., Conceicao, M., Montenegro, B. S. M.: Talanta 72 (2007) 13 [2]Byrne, R., Diamond D., Nature Materials 5(6) (2006) 421

Izvorni jezik
Engleski

Znanstvena područja
Kemija, Elektrotehnika, Kemijsko inženjerstvo

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