Screen-printed interdigitated microelectrodes employment in dielectrophoretic manipulation of MWCNTs

As key enablers of Industry 4.0 and Internet of Things, sensors are among the first devices which are to encounter fast physical transformation (from rigid to flexible) as of large-scale utilization of printing technologies. In order to step-up this process, adaptation of conventional fabrication technologies (based on metallization) employed in sensors' development should be tested and demonstrated. Within this paper, we are reporting the functionality of dielectrophoresis (DEP) for electromanipulation of multi-walled carbon nanotubes (MWCNTs) as sensing element, at the level of printed interdigitated electrodes. First, we present the flatbed screen-printed process of interdigitated microelectrodes on flexible substrate with tailored geometries employed afterwards for generating convenient dielectrophoretic forces of optimal magnitude and frequency for trapping MWCNTs. Successful dielectrophoresis operability of MWCNTs across silver-based screen-printed μIDE (interdigitated microelectrodes) provided with electrode gaps of ≈ 150 μm was validated and suitable values of the signal frequencies for avoiding parasitic electrokinetic phenomena (AC electro-osmosis, electrothermal effect) occurring simultaneously with DEP were identified. Time-dependent effect of DEP over MWCNTs bridges formation is discussed, as well as voltage magnitude contribution.

Gold interdigitated triple-microelectrodes for label-free prognosticative aptasensing of prostate cancer biomarker in serum

A simple, single-masked gold interdigitated triple-microelectrodes biosensor is presented by taking the advantage of an effective self-assembled monolayer (SAM) using an amino-silanization technique for the early detection of a prostate cancer's biomarker, the prostate-specific antigen (PSA). Unlike most interdigitated electrode biosensors, biorecognition happens in between the interdigitated electrodes, which enhances the sensitivity and limit of detection of the sensor. Using the Faradaic mode electrochemical impedance spectroscopy (EIS) technique to quantify the PSA antigen, the developed sensing platform demonstrates a logarithmic detection of PSA ranging from 0.5 ng/ml to 5000 ng/ml, an estimated LOD down to 0.51 ng/ml in the serum, and a good sensor's reproducibility. The sensor's detection range covers the clinical threshold value at 4 ng/ml and the crucial diagnosis 'grey zone' of 4-10 ng/ml of PSA in serum for an accurate cancer diagnosis. The selectivity test revealed an excellent discrimination of other competing proteins, with a recorded detection signals at 5 ng/ml PSA as high as 7-fold increase versus the human serum albumin (HSA) and 8-fold increase versus the human glandular kallikrein 2 (hK2). The stability test showed an acceptable stability of the aptasensor recorded at six (6) days before the detection signal started degrading below 10% of the peak detection value. The developed sensing scheme is proven to exhibit a great potential as a portable prostate cancer biosensor, also as a universal platform for bio-molecular sensing with the versatility to implement nanoparticles and other surface chemistry for various applications.

Electrochemical detection of food-spoiling bacteria using interdigitated platinum microelectrodes

The fast and non-destructive detection of bacterial attachment on food contact surfaces is important for the prevention of the unwanted formation of biofilms. Biofilms constitute a protected growth mode that allows bacteria to survive even in hostile environments. Therefore, the fast detection of bacterial attachment may be an effective strategy for biofilm control. In this study cyclic voltammetry (CV) was used to detect Bacillus subtilis ssp. subtilis, Paenibacillus polymyxa, Pseudomonas fragi attachment on interdigitated microelectrodes. The differences in current between the uncolonized sterile microelectrodes and the microelectrodes after bacterial attachment were determined. In addition, the surface coverage of microelectrodes was visualized using microscopy techniques. The results showed that the cyclic voltammetry in combination with interdigitated platinum microelectrodes can be used to detect bacterial biofilms.

Impedimetric detection of bacteria by using a microfluidic chip and silver nanoparticle based signal enhancement

The authors describe a method that can significantly improve the performance of impedimetric detection of bacteria. A multifunctional microfluidic chip was designed consisting of interdigitated microelectrodes and a micro-mixing zone with a Tesla structure. This maximizes the coating of bacterial surfaces with nanoparticles and results in improved impedimetric detection. The method was applied to the detection of Escherichia coli O157:H7 (E. coli). Silver enhancement was accomplished by coating E.coli with the cationic polymer diallyldimethylammonium chloride (PDDA) to form positively charged E. coli/PDDA complexes. Then, gold nanoparticles (AuNPs) were added, and the resulting E. coli/PDDA/AuNPs complexes were collected at interdigitated electrodes via positive dielectrophoresis (pDEP). A silver adduct was then formed on the E. coli/PDDA/AuNP complexes by using silver enhancement solutions and by using the AuNPs as catalysts. The combination of pDEP based capture and of using silver adducts reduces impedance by increasing the conductivity of the solution and the double layer capacitance around the microelectrodes. Impedance decreases linearly in the 2 × 10³-2 × 10⁵ cfu·mL^-1 E. coli concentration range, with a 500 cfu·mL^-1 detection limit. Egg shell wash samples and tap water spiked with E. coli were successfully used for validation, and this demonstrates the practical application of this method. Graphical abstract Schematic representation of the AuNP@Ag enhancement method integrated with multifunctional microfluidic chip platform for impedimetric quantitation of bacteria. The method significantly improves the performance of impedimetric detection of bacteria.

Simultaneous monitoring of Staphylococcus aureus growth in a multi-parametric microfluidic platform using microscopy and impedance spectroscopy

We describe the design, construction, and characterization of a scalable microfluidic platform that allows continuous monitoring of biofilm proliferation under shear stress conditions. Compared to other previous end-point assay studies, our platform offers the advantages of integration into multiple environments allowing simultaneous optical microscopy and impedance spectroscopy measurements. In this work we report a multi-parametric sensor that can monitor the growth and activity of a biofilm. This was possible by combining two interdigitated microelectrodes (IDuEs), and punctual electrodes to measure dissolved oxygen, K+, Na+ and pH. The IDuE has been optimized to permit sensitive and reliable impedance monitoring of Staphylococcus aureus V329 growth with two- and four-electrode measurements. We distinguished structural and morphological changes on intact cellular specimens using four-electrode data modeling. We also detected antibiotic mediated effects using impedance. Results were confirmed by scanning electrode microscopy and fluorescence microscopy after live/dead cell staining. The bacitracin mediated effects detected with impedance prove that the approach described can be used for guiding the development of novel anti-biofilm agents to better address bacterial infection.

Conductometric Microbiosensors for Environmental Monitoring

This review presents the principles of conductometric measurements in ionic media and the equivalent electrical circuits of different designs for conductometric measurements. These types of measurements were first applied for monitoring biocatalytic reactions. The use of conductometric microtransducers is then presented and detailed in the case of pollutant detection for environmental monitoring. Conductometric biosensors have advantages over other types of transducers: they can be produced through inexpensive thinfilm standard technology, no reference electrode is needed and differential mode measurements allow cancellation of a lot of interferences. The specifications obtained for the detection of different pesticides, herbicides and heavy metal ions, based on enzyme inhibition, are presented as well as those obtained for the detection of formaldehyde, 4- chlorophenol, nitrate and proteins as markers of dissolved organic carbon based on enzymatic microbiosensors.