Electrochemical and viscoelastic evolution of dodecyl sulfate-doped polypyrrole films during electrochemical cycling

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Authors: Wanli Gao, Ozlem Sel, Hubert Perrot

Journal:  Electrochimica Acta (2017)

The correlation between electrochemical and viscoelastic properties of electrodeposited dodecysulfatedoped polypyrrole (PPy-DS) during electrochemical cycling process was described through combining electrochemical quartz-crystal microbalance (EQCM), ac-electrogravimetric characterizations and electroacoustic measurements. as the PPy-DS electrode evolves during the course of consecutive cycling in aqueous NaCI electrolyte, the film exhibits (i) an obvious ion-selective transition from cations to anions in the charge compensation process; (ii) an inferior electrochemical performance accompanied with increased stiffness (increased storaged moduli, G’); and (iii) depleted capability of ionic exchange through film/electrolyte interface. PPy-DS conducting polymer electrodes (CPEs) are of interest in energy storage and the relationship between electrochemical and viscoelastic properties during electrochemical cycling process is essential for promoting the performance of these devices. In this perspective, ac-electrogravimetry combined with electroacoustic measurements can be suggested as an alternative method to synchronously probe the electrochemical and mechanical evolution and has the potential to offer a generalized route to study aging mechanism of CPEs.

 

pH Controlled Electrochemical Deposition of Polyelectrolyte Complex Films

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Authors: Kazi Sadman, Qifeng Wang, Shawn H Chen, David Efim Delgado and Kenneth R Shull. Northwestern University, Evanston, Illinois, US

Journal:  Langmuir 2017, 33(8) 1834-1844.

Abstract: Polyelectrolyte complex (PEC) films made from oppositely charged polymer chains have applications as drug delivery vehicles, separation membranes, and biocompatible coatings. Conventional layer-by-layer (LbL) techniques for polyelectrolyte coatings are low-throughput and multistep processes that are quite slow for building films on the order of micrometers. In this work, PEC films are electrochemically deposited using a rapid one-pot method yielding thick (1 μm) films within short experimental time scales (5 min). This rapid electrodeposition is achieved by exploiting the reduction of hydrogen peroxide at mild electrode potentials that avoid water electrolysis, yet trigger the pH responsive self-assembly of a PEC film composed of poly(acrylic) acid and poly (allylamine) HCl. In-situ rheology using an electrochemical quartz crystal microbalance (EQCM) quantified the shear modulus-density product of the deposited layer to be on the order of 107 Pa-g/cm3 at a frequency of 15 MHz, with a viscoelastic phase angle at this frequency of approximately 50○. This electrodeposition scheme furthers the development of PEC coatings for more high-throughput applications where a fast and efficient single step approach would be desirable for obtaining coatings.

Link: https://doi.org/10.1021/acs.langmuir.6b04491

Gravimetric and dynamic deconvolution of global EQCM response of carbon nanotube based electrodes by Ac-electrogravimetry

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Authors: F. Escobar-Teran, A. Arnau, J.V. García, Y. Jiménez, H. Perrot, O. Sel

Journal: Electrochemistry communications (2016)

The capacity charge storage of carbon nanotube (CNT) based electrodes was investigated by ac-electrogravimetry which couples fast quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy (EIS). In contact with an aqueous NaCI electrolyte, evidence was found that there are two types of cations (Na+.H2O and H+) electroadsorbed with different kinetics for cathodic potentials and the Cl– ionsfor anodic potentials together with free water molecules. The reconstruction of the total mass response from independent ac-electrogravimetry measurements agrees perfectly well with the global EQCM response. Our findings reveal the unique sensitivity of the ac-electrogravimetry to provide a fair gravimetric and dynamic deconvolution of the global EQCM responses.

You may read the full paper here

Calcium-induced calmodulin conformational change. Electrochemical evaluation

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Authors: Isabel P.G. Fernandes, Ana Maria Oliveira-Brett. Chemistry Department, Faculty of Sciences and Technology, University of Coimbra, 3004-535 Coimbra, Portugal.

Journal: Bioelectrochemistry (2016)

Calmodulin (CaM) is an essential protein present in all eukaryote cells, ranging from vertebrates to unicellular organisms. CaM is the most important Ca2+ signalling protein, composed of two domains,  N- and C-terminal domains, linked by a flexible central α – helix, and is responsible for the regulation of numerous calcium-mediated signalling pathways. Four calcium ions bind to CaM, changing its conformation and determining how it recognizes and regulates its cellular targets. The oxidation mechanism of native and denatured CaM, at a glassy carbon electrode, was investigated using differential pulse voltammetry and electrochemical impedance spectroscopy. Native and denatured CaM presented only one oxidation peak, related to the tyrosine amino acid residue oxidation. Calcium-induced calmodulin conformational change and the influence of Ca2+ concentration on the electrochemical behaviour of CaM were evaluated, and significant differences, in the tyrosine amino acid residue peak potential and current, in the absence and in the presence of calcium ions, were observed. Gravimetric measurements were performed with a graphite coated piezoelectric quartz crystal with adsorbed CaM and calcium aggregation by CaM was demonstrated.

You may read the full paper here

HFF-QCM immunosensor for fast and sensitive detection of DDT in honey

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Summary

The control of chemical residues is essential in honey’s marketing to ensure consumer safety. Equipments available in the market reach the required limit of detection (LOD) (e.g. Liquid Cromatography- HPLC) but are not suitable for in-situ implantation in honey packaging industry. The reasons are:

  • High qualified staff required
  • High cost
  • Time-consuming

Other approaches available in the market, although faster and without the need of qualified staff, do not reach the required LODs. Piezoelectric immunosensors based on High Fundamental Frequency Quartz Crystal Microbalance (HFF-QCM) combined with an antigen-antibody recognition process, are alternative or complementary technologies suitable for chemical residues control in food.

The analytical performance of AWS-A20 and AWS-F20 platforms (based on HFF-QCM technology) has been tested for the detection of pesticide residues (DDT) in honey.

AWS platforms lead to the following benefits:

  • Lower cost
  • Less sample/reagent consumption
  • Label-free, direct and real time transduction

DDT standard curves performed in laboratory buffer provided:

  • Sensitivity (estimated as the I50 value): 0.62 µg/L
  • LOD in the 0.05 – 0.1 µg/L range

Remarks

  • A HFF-QCM immunosensors for DDT insecticide has been developed
  • Efficient biosensing interfaces were achieved by covalent functionalization of the sensor gold electrodes with mixed alkane-thiol self-assembled monolayers (mSAMs)
  • High-sensitivity monoclonal antibodies were used as the bio-recognition element of the target analyte in a competitive immunoassay format.
  • The limits of detection (LOD) and quantification (LOQ) and the working range (WR) of the developed HFF-QCM immunosensor for DDT are in the same order of magnitude as those previously reported for ELISA and SPR immunosensor.

 

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High-frequency phase shift measurements greatly enhances the sensitivity of QCM immunosensors

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Authors: C. March, J.V. García, A. Sánchez, A. Arnau, Y. Jiménez, P. García, J.J. Manclús, A. Montoya.

Journal: Biosensors & Bioelectronics (2015)

In spite of being widely used for in liquid biosensing applications, sensitivity improvement of conventional (5-20MHz) quartz crystal microbalance (QCM) sensors remains an unsolved challenging task. With the help of a new electronic characterization approach based on phase change measurements at a constant fixed frequency, a highly sensitive and versatile high fundamental frequency (HFF) QCM immunosensor has successfully been developed and tested for its use in pesticide (carbaryl and thiabendazole) analysis. The analytical performance of several immunosensors was compared in competitive immunoassays taking carbaryl insecticide as the model analyte. The highest sensitivity was exhibited by the 100 MHz HFF-QCM carbaryl immunosensor. When results were compared with those reported for 9 MHz QCM, analytical parameters clearly showed an improvement of one order of magnitude for sensitivity (estimated as the I50value) and two orders of magnitude for the limit of detection (LOD): 30 μg l−1 vs 0.66 μg L−1I50 value and 11 μg L−1 vs 0.14 μg L−1 LOD, for 9 and 100 MHz, respectively. For the fungicide thiabendazole, I50 value was roughly the same as that previously reported for SPR under the same biochemical conditions, whereas LOD improved by a factor of 2. The analytical performance achieved by high frequency QCM immunosensors surpassed those of conventional QCM and SPR, closely approaching the most sensitive ELISAs. The developed 100 MHz QCM immunosensor strongly improves sensitivity in biosensing, and therefore can be considered as a very promising new analytical tool for in liquid applications where highly sensitive detection is required.

 

Further sensitivity enhancement of HFF-QCM immunosensors for pesticides

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Authors: C. March, J.V. García, R. Fernández, Y.Jiménez, A. Arnau. A.Montoya

Event: 4th International Conference on Biosensing Technology, Lisbon (2015)

Recently, High Fundamental Frequency Quartz Crystal Microbalance (HFF-QCM) immunosensors have succesfully been developed. Therefore, sensitivity of QCM biosensors is no longer a drawback. Taking advantage of this previous work, we have developed a renewed highly sensitive HFF piezoelectric immunosensor using carbaryl insecticide as a model analyte for pesticide detection. To this purpose, 100 MHz quartz crystal sensors were used as the transducer elements of the biosensor and a monoclonal antibody-based competitive immunoassay was integrated as the sensing specific bio-recognition event. The biosensing interface was improved by employing mixed self-assembled monolayers (mSAMs) of alkane thiols as intermediate layers for surface functionalization. This approach allowed the covalent attachment of the assay conjugate (20.0 µg mL-¹ of BSA-CNH conjugate) onto the gold electrode surface in a more orderly and stable way than with simple SAMs. A very low concentration (1.0 µg mL-¹) of LIB-CNH45 monoclonal antibody was used for the competitive immunoassays. All immunosensor assays were performed in the AWS-A10 test platform from AWSensors. In terms of analytical performance, the new carbaryl HFF-QCM immunosensor showed higher sensitivity than the previously developed one, with analytical parameters very close to those of the most sensitive reported ELISA for carbaryl.

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Development of a High Fundamental Frequency (HFF) Piezoelectric Immunosensor for early and sensitive detection of tuberculosis

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Authors: A. Montoya, C. March, Y.J. Montagut, M.J. Moreno, J.J. Manclús, A. Arnau, Y. Jiménez, M. Jaramillo, P.A. Marín, R.A. Torres.

Event: International Work-Conference on Bioinformatics and Biomedical Engineering, IWBBIO 2015, Granada (Spain), April 15-17, 2015. (2015)

Tuberculosis is one of the oldest diseases affecting human beings and at present it is still considered as a world public health problem, both in developing and in developed countries. Consequently, the World Health Organization encourages the development of new and more powerful analytical methods able to sensitively detect tuberculosis biomarkers in order to provide early diagnosis and treatment.

Taking advantage of the most recent advances in new detection technologies, such as biosensors and particularly immunosensors, in the present paper we describe the development of a High Fundamental Frequency (HFF) piezoelectric immunosensor for the sensitive detection of tuberculosis. First, a secretion protein (38 kDa) from Mycobacterium tuberculosis was selected as the tuberculosis biomarker. Next, high affinity monoclonal antibodies (MAbs) specific to the target analyte were obtained. To this purpose, a recombinant form of the 38 kDa protein was used as immunizing antigen and hybridoma technology was subsequently applied for antibody production. The best MAb (namely Myc-31) was employed as the primary immunoreagent for the development of an enzyme-linked immunosorbent assay (ELISA) for 38 kDa quantification. This ELISA reached a detection limit as low as 0.014 μg mL-1 of the 38 kDa antigen and was used as a previous diagnostic test and reference assay for the future biosensor.

Finally, the HFF piezoelectric immunosensor for 38 kDa detection and quantification was developed. High fundamental frequency (100 MHz) quartz crystals were used as the transducer elements of the biosensor. Crystals were functionalized by covalent immobilization of the 38 kDa antigen onto the gold electrode surface of the quartz crystal. Mixed self-assembled monolayers (mSAM) of alkane- thiols and acids were used as intermediate layers for immobilization. A monoclonal antibody-based competitive immunoassay was then integrated as the sensing specific bio-recognition event coupled to the transducer. With this aim, the concentration of the 38 kDa antigen for immobilization and the limiting amount of the MAb for the competitive assay were previously optimized. All immunosensor assays were performed in the AWS A10 platform developed by AWSensors. As expected for HFF piezoelectric transducers, high and stable assay signals were obtained using very low protein concentrations for crystal functionalization (20 μg mL-1 of the 38 kDa antigen) and for the competitive immunoassay (0.75 μg mL-1 of Myc-31 MAb).

Under these conditions, the HFF immunosensor calibration curve for the determination of the 38 kDa antigen was performed by assaying different biomarker concentrations in the [ng mL-1 – mg mL-1] range. Each assay cycle took around 25 min including regeneration of the functionalized sensor surface between assays.

Regeneration was achieved by treatment with 0.01 M HCl. Figure 1 depicts the average 38 kDa standard curve obtained from several experiments using different 100 MHz crystals. It shows the typical decreasing sigmoidal shape associated to competitive assays.

Figure 1: Calibration curve of the HFF piezoelectric immunosensor for the 38 kDa biomarker

The IC50 value of the competitive standard curve (analyte concentration producing a 50% inhibition of the maximum assay signal, which is in turn considered as an estimate of the assay sensitivity in immunoassays) was 0.080 μg mL-1 of the 38 kDa antigen. The limit of detection of the HFF immunosensor (calculated as the analyte concentration providing a 10% inhibition of the maximum assay signal) was around 0.011 μg mL-1 of the 38 kDa biomarker, even lower than that of the previously developed ELISA. The high detectability attained by this immunosensor, in the picomolar range, makes it a very promising tool for the easy, direct and sensitive detection of the tuberculosis biomarker in biological fluids such as sputum.

Keywords: 38 kDa tuberculosis biomarker; Monoclonal antibody; ELISA; High Fundamental Frequency (HFF); Piezoelectric Immunosensor.

Publication on AWSensors technology

Love Mode Surface Acoustic Wave and High Fundamental Frequency QCM Immunosensors for the Detection of Carbaryl Pesticide

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Authors: J.V. García, M.I. Rocha, C. March, P. García, L.A. Francis, A. Montoya, A. Arnau, Y. Jiménez

Event: Eurosensors XXVIII Conference. Brescia, Italia (2014)

 

In this work we determined the Sensitivity (estimated as the I50 value) and Limit of Detection (LOD) for the immunodetection of carbaryl pesticide with two different types of acoustic wave sensors: High Fundamental Frequency QCM Quartz Crystal Microbalance (HFF-QCM) and Love Mode Surface Acoustic Wave (LM-SAW). Results were compared with others previously reported using different sensors and techniques, like traditional QCM, Surface Plasmon Resonance (SPR) and Enzyme-Linked ImmunoSorbent Assay (ELISA). We used the AWS-A10 research platform (AWSensors, Spain) to perform the experiments. We obtained I50 values of 0.31 μg/L and 0.66 μg/L, and LODs of 0.09 μg/L and 0.14 μg/L, for 120 MHz LM-SAW and 100 MHz HFF-QCM devices, respectively. Both the sensitivities and LODs of the immunosensors improved previously reported SPR and QCM results by one and two orders of magnitude, respectively, and reached those of ELISA.

Love Wave Immunosensor for the detection of carbaryl pesticide

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Authors: M. Rocha-Gaso, J.V. García, P. García, C. March, Y. Jiménez, L.A. Francis, A.I Montoya, A. Arnau

Journal: Sensors (2014)

 

A Love Wave (LW) immunosensor was developed for the detection of carbaryl pesticide. The experimental setup consisted on: a compact electronic characterization circuit based on phase and amplitude detection at constant frequency; an automated flow injection system; a thermal control unit; a custom-made flow-through cell; and Quartz /SiO2 LW sensors with a 40 μm wavelength and 120 MHz center frequency. The carbaryl detection was based on a competitive immunoassay format using LIB-CNH45 monoclonal antibody (MAb). Bovine Serum Albumin-CNH (BSA-CNH) carbaryl hapten-conjugate was covalently immobilized, via mercaptohexadecanoic acid self-assembled monolayer (SAM), onto the gold sensing area of the LW sensors. This immobilization allowed the reusability of the sensor for at least 70 assays without significant signal losses. The LW immunosensor showed a limit of detection (LOD) of 0.09 μg/L, a sensitivity of 0.31 μg/L and a linear working range of 0.14–1.63 μg/L. In comparison to other carbaryl immunosensors, the LW immunosensor achieved a high sensitivity and a low LOD. These features turn the LW immunosensor into a promising tool for applications that demand a high resolution, such as for the detection of pesticides in drinking water at European regulatory levels.