In this work we have developed an amperometric enzymatic biosensor in a paper-based platform with a mixed electrode configuration: carbon ink for the working electrode (WE) and metal wires (from a low-cost standard electronic connection) for reference (RE) and auxiliary electrodes (AE). A hydrophobic wax-defined paper area was impregnated with diluted carbon ink. Three gold-plated pins of the standard connection are employed, one for connecting the WE and the other two acting as RE and AE. The standard connection works as a clip in order to support the paper in between. As a proof-of-concept, glucose sensing was evaluated. The enzyme cocktail (glucose oxidase, horseradish peroxidase and potassium ferrocyanide as mediator of the electron transfer) was adsorbed on the surface. After drying, glucose solution was added to the paper, on the opposite side of the carbon ink. It wets RE and AE, and flows by capillarity through the paper contacting the carbon WE surface. The reduction current of ferricyanide, product of the enzymatic reaction, is measured chronoamperometrically and correlates to the concentration of glucose. Different parameters related to the bioassay were optimized, adhering the piece of paper onto a conventional screen-printed carbon electrode (SPCE). In this way, the RE and the AE of the commercial card were employed for optimizing the paper-WE. After evaluating the assay system in the hybrid paper-SPCE cell, the three-electrode system consisting of paper-WE, wire-RE and wire-AE, was employed for glucose determination, achieving a linear range between 0.3 and 15mM with good analytical features and being able of quantifying glucose in real food samples.

In this work, bifunctional core@shell Au@Pt/Au NPs are presented as novel tags for electrochemical immunosensing.Au@Pt/Au NPs were synthesized following a chemical route based on successive metal depositions and galvanic replacement reactions from the starting AuNPs. Au protuberances growth on the surface of Au@Pt NPs allowed their easy bioconjugation with antibodies, while the high catalytic Pt surface area was approached for their sensitive detection through the electrocatalysed water oxidation reaction (WOR) at neutral pH. Moreover, the synergy between Au and Pt metals on the NP surface also lead to an increased catalytic activity, improving the sensitivity of the NP detection. Cyclic voltammetry and chronoamperometry were used for the evaluation of the Au@Pt/Au NPs electrocatalytic activity towards WOR. The chronoamperometric current recorded at a fixed potential of +1.35 V was selected as the analytical signal, allowing the quantification of Au@Pt/Au NPs at 10 13 NPs/mL levels. The optimized electrocatalytic method was applied to the quantification of conformationally altered p53 peptide Alzheimer's disease (AD) biomarker in a competitive immunoassay using magnetic bead (MB) platforms at levels as low as 66 nM. The performance of the system in a real scenario was demonstrated analysing plasma samples from a cognitively healthy subject. This novel Au@Pt/Au NPs-based electrocatalytic immunoassay has the advantage, over common methods for NP tags electrochemical detection, of the signal generation in the same neutral medium where the immunoassay takes place (0.1 M PBS pH 7.2), avoiding the use of additional and more hazardous reagents and paving the way to future integrated biosensing systems. 38 trolled synthesis, higher stability against harsh conditions, 39 higher resistance to high concentrations of substrate and a lower 40 cost [3][4][5][6] . The use of electrocatalytic NPs as labels has been ex-41 tensively studied and applied in immunosensing [7][8][9][10][11][12] , offering 42 outstanding alternatives to traditional assays. 43Among the wide variety of NPs, metallic NP labels have at-44 tracted considerable interest due to their unique red-ox and op-45 tical properties 13,14 as well as their electrocatalytic activity, also 46 benefiting of the inherent advantages of the electrochemical de-47 tection in terms of sensitivity, selectivity, simplicity and low 48 cost 15 . In most cases highly acidic media are needed for such 49 NPs detection, either to facilitate dissolution 16 or as source of 50 hydrogen ions for further detection based on hydrogen evolu-51 tion reaction (HER) [17][18][19][20][21][22][23] . However, the use of acid solutions is 52 not desirable for both safety reasons and the time needed for the 53 analysis, also involving additional steps after the immunoassay. 54Consequently, there is a need of NP tags that may be detected 55 in the same medium where immunoreactions take place. In this 56 context, the water oxidation reaction (WOR) occurring at neu-57 tral pH and easily catalysed by some ...

This lab experiment describes a complete 6 method to fabricate an enzymatic glucose electroanalytical 7 biosensor by students. Using miniaturized and disposable 8 screen-printed electrodes (SPEs), students learn how to use 9 them as transducers and understand the importance SPEs have 10 .jchemed.6b00948 J. Chem. Educ. XXXX, XXX, XXX−XXX rdk00 | ACSJCA | JCA10.0.1465/W Unicode | research.3f (R3.6.i12 HF02:4458 | 2.0 alpha 39) 2016/10/28 09:46:00 | PROD-JCAVA | rq_8339184 | 3/22/2017 11:04:37 | 7 | JCA-DEFAULT a Data are given as mean ± SD calculated with two degrees of freedom and p = 0.05; n = 3. Salimi, A.; Abdi, K.; Khayatian, G. R. Amperometric detection of 487 dopamine in the presence of ascorbic acid using a nafion coated glassy 488 carbon electrode modified with catechin hydrate as a natural 489 antioxidant.

This review shows recent trends in the use of nanoparticles as labels for electrochemical immunosensing applications. Some general considerations on the principles of both the direct detection based on redox properties and indirect detection through electrocatalytic properties, before focusing on the applications for mainly proteins detection, are given. Emerging use as blocking tags in nanochannels-based immunosensing systems is also covered in this review. Finally, aspects related to the analytical performance of the developed devices together with prospects for future improvements and applications are discussed.

In this work, we present a multiplexed (eight simultaneous measurements) paperbased electrochemical device developed in a very simple way and using low-cost materials, such as paper, carbon ink and multifunctional connector headers.Meanwhile, we have also combined the paper-based electrochemical platform with a glass-fiber strip in order to integrate easily a sampling step. Both approaches, simultaneous measuring and sampling, have been applied to the determination of glucose using bienzymatic biosensors. They are fabricated by adsorbing the mixture of enzymes (glucose oxidase and horseradish peroxidase), as well as the ferrocyanide, mediator of the electron transfer, on the paper-based electrode. After drying, the measuring solution (containing either glucose standards or samples) is added and the eight corresponding chronoamperograms are recorded. In the case of the microfluidic approach for sampling purposes, the glass-fiber pad (sampler) is immersed in a container with the solution, which flows by capillarity until it reaches the working electrode. The integration of one more step of the analytical process advances towards real and useful lab-on-a-chip devices. With these designs, a linear range comprised between 0.5 and 15 mM was achieved for glucose determination, with excellent precision. If the sampler is employed, it is not necessary to use micropipettes and, nevertheless, precise measurements are obtained. The RSD of the slopes obtained for different calibrations performed in different days, with different arrays of electrochemical cells and different solutions is ca. 1%. Accurate results are obtained in the determination of glucose in real samples (orange fruit and cola beverages).