Sensors and Actuators B 210 (2015) 183–189 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical jo ur nal home page: www.elsevier.com/locate/snb Bipolar transistor amplifier for transduction of electrochemical response to visual perception Karel Lacina a,∗ , Petr Skládal a,b a CEITEC, Masaryk University, Kamenice 5, Brno 625 00, Czech Republic b Department of Biochemistry, Faculty of Science, Masaryk University, Kamenice 5, Brno 625 00, Czech Republic a r t i c l e i n f o Article history: Received 2 October 2014 Received in revised form 17 December 2014 Accepted 27 December 2014 Available online 6 January 2015 Keywords: Simple electrochemical detection Electrochemical transduction Point-of-care diagnostics Transistor Visual readout a b s t r a c t A simple device for the transduction of an electrochemical signal to a visual readout suitable for point of care diagnostics has been designed. The transducer consists of an electrochemical cell and a 4-electronic components circuit, namely two resistors, one transistor and one light emitting diode (LED). The response from the electrochemical cell is amplified by the transistor providing output for the direct visual readout with the naked eye. Function of the device was verified in the experiments with hydrogen peroxide. Sim- ple adjustment of the values of resistors provided tuneable sensitivity, positive threshold level and limit of detection as well. The biosensing abilities of the proposed system were tested on the analytical model using immobilised glucose oxidase. The principal benefits of the proposed platform include uniquely low construction costs and high simplicity. This approach is innovative in the transduction/conversion of the signal to visual perception and also in the signal generation – no potentiostat nor galvanostat are used compared to the majority of electrochemical measurements. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Point-of-care (POC) diagnostics is an attractive analytical approach which is nowadays rapidly developing. Its merit stems from the transfer of an analytical act from a specialised laboratory close to the patient or generally directly to the site of sample col- lection. The production costs of analytical devices based on POC principles should be preferentially low resulting in low cost of one analysis. Furthermore, portability and simple operation are neces- sary and the obtained results should be suitable for straightforward interpretation even by unskilled person and without any operation manual [1,2]. A paper indicator still remains the simplest analytical POC sys- tem, e.g. litmus paper and urine test strips. Its main advantage originates from the construction material used paper. Cheap- ness, elasticity, temperature and dimensional stability, high liquid absorption, porous structure, capillary action, high ratio of active surface to volume, biocompatibility and simple degradability (either incineration or biodegradation) all belong to the favourable properties [2–4]. Devices based on paper substrate are highly suit- able for disposable sensors; the low cost of one analysis is related ∗ Corresponding author. Tel.: +420 54949 7611. E-mail address: lacinak@chemi.muni.cz (K. Lacina). to the possibility of mass production. The detection ranges are at milimolar concentrations for low molecular clinical analytes as glucose, lactate and uric acid [5,6]. Systems reaching sub- milimolar concentrations were reported for particular analytes, however, specialised instruments (readers) were necessary for the precise readout of the signal [7]. With some exceptions the obtained analytical information is principally in the YES/NO for- mat. Complex instruments which contain sophisticated electronics with potentiostat, microcomputer, display, software etc. [8] are on the opposite side of the spectrum of POC devices. These instru- ments exhibit high flexibility of measurement performance and complexity of the generated data. They are able to provide many measuring approaches, possibility to detect several analytes upon relatively undemanding modification of system, high sensitivity, the obtained value of concentration of an analyte is visualised as a number on the display and the possibility of local data storage and nowadays also the popular transfer to internet-based cloud systems is usually provided. The last option allows remote interpre- tation by expert and re-sending the decision back to “the sampling point”. The higher price and operating costs are common disad- vantages of these instruments. The handling and operation need not to be necessarily simple. Moreover, with the increasing com- plexity of the instrument, the probability of a malfunction grows as well. http://dx.doi.org/10.1016/j.snb.2014.12.110 0925-4005/© 2015 Elsevier B.V. All rights reserved.