Introducing Thermal Wave Transport Analysis (TWTA): A Thermal Technique for Dopamine Detection by Screen-Printed Electrodes Functionalized with Molecularly Imprinted Polymer (MIP) Particles.

A novel procedure is developed for producing bulk modified Molecularly Imprinted Polymer (MIP) screen-printed electrodes (SPEs), which involves the direct mixing of the polymer particles within the screen-printed ink. This allowed reduction of the sample preparation time from 45 min to 1 min, and resulted in higher reproducibility of the electrodes. The samples are measured with a novel detection method, namely, thermal wave transport analysis (TWTA), relying on the analysis of thermal waves through a functional interface. As a first proof-of-principle, MIPs for dopamine are developed and successfully incorporated within a bulk modified MIP SPE. The detection limits of dopamine within buffer solutions for the MIP SPEs are determined via three independent techniques. With cyclic voltammetry this was determined to be 4.7 × 10−6 M, whereas by using the heat-transfer method (HTM) 0.35 × 10−6 M was obtained, and with the novel TWTA concept 0.26 × 10−6 M is possible. This TWTA technique is measured simultaneously with HTM and has the benefits of reducing measurement time to less than 5 min and increasing effect size by nearly a factor of two. The two thermal methods are able to enhance dopamine detection by one order of magnitude compared to the electrochemical method. In previous research, it was not possible to measure neurotransmitters in complex samples with HTM, but with the improved signal-to-noise of TWTA for the first time, spiked dopamine concentrations were determined in a relevant food sample. In summary, novel concepts are presented for both the sensor functionalization side by employing screen-printing technology, and on the sensing side, the novel TWTA thermal technique is reported. The developed bio-sensing platform is cost-effective and suitable for mass-production due to the nature of screen-printing technology, which makes it very interesting for neurotransmitter detection in clinical diagnostic applications

Development of a Flexible MIP-Based Biosensor Platform for the Thermal Detection of Neurotransmitters

We have developed high affinity Molecularly Imprinted Polymers (MIPs) for neurotransmitters such as dopamine, noradrenaline and caffeine. These polymer particles are mixed within the bulk of screen-printed ink allowing masss-producible bulk modified MIP Screen-Printed Electrodes (MIP-SPEs) to be realised. We have explored different SPE supporting surfaces, such as polyester, tracing paper and household-printing paper. The performance of those MIP-SPEs is studied using the Heat-Transfer Method (HTM), a patented thermal method. With the combination of screen-printing techniques and thermal detection, it is possible to develop a portable sensor platform that is capable of low-cost and straightforward detection of biomolecules on-site. In the future, this unique sensor architecture holds great promise for the use in biomedical devices

Real-time analysis of microbial growth by means of the Heat-Transfer Method (HTM) using Saccharomyces cerevisiae as model organism

In this manuscript, we explore the use of the Heat-Transfer Method (HTM) for the real-time analysis of microbial growth using Saccharomyces cerevisiae as a model organism. The thermal responses of gold electrodes upon exposure to suspensions of S. cerevisiae (wild type strain DLY640) concentrations were monitored, demonstrating an increase in thermal resistance at the solid-liquid interface with higher concentrations of the microorganism. Flow cells were manufactured using 3D-printing to facilitate longitudinal experiments. We can clearly discriminate between the growth of S. cerevisiae under optimal conditions and under the influence of factors that inhibit the replication process, such as the use of nutrient depleted growth medium, elevated temperature, and the presence of toxic compounds. In addition, it is possible to determine the kinetics of the growth process and quantify yeast replication which was demonstrated by measuring a mutant temperature sensitive strain. This is the first time HTM has been used for the real-time determination of factors that impact microbial growth. Thermal sensing is low-cost, offers straightforward analysis and measurements can be performed on-site. Due to the versatility of this method, this platform can be extended to monitor other microorganisms and in particular to study the response of bacteria to selected antibiotics

Label-Free Detection of Escherichia coli Based on Thermal Transport through Surface Imprinted Polymers

This work focuses on the development of a label-free biomimetic sensor for the specific and selective detection of bacteria. The platform relies on the rebinding of bacteria to synthetic cell receptors, made by surface imprinting of polyurethane-coated aluminum chips. The heat-transfer resistance (Rth) of these so-called surface imprinted polymers (SIPs) was analyzed in time using the heat-transfer method (HTM). Rebinding of target bacteria to the synthetic receptor led to a measurable increase in thermal resistance at the solid–liquid interface. Escherichia coli and Staphylococcus aureus were used as model organisms for several proof-of-principle experiments, demonstrating the potential of the proposed platform for point-of-care bacterial testing. The results of these experiments indicate that the sensor is able to selectively detect bacterial rebinding to the SIP surface, distinguishing between dead and living E. coli cells on one hand and between Gram-positive and Gram-negative bacteria on the other hand (E. coli and S. aureus). In addition, the sensor was capable of quantifying the number of bacteria in a given sample, enabling detection at relatively low concentrations (104 CFU mL–1 range). As a first proof-of-application, the sensor was exposed to a mixed bacterial solution containing only a small amount (1%) of the target bacteria. The sample was able to detect this trace amount by using a simple gradual enrichment strategy

A Novel Biomimetic Tool for Assessing Vitamin K Status Based on Molecularly Imprinted Polymers

Vitamin K was originally discovered as a cofactor required to activate clotting factors and has recently been shown to play a key role in the regulation of soft tissue calcification. This property of vitamin K has led to an increased interest in novel methods for accurate vitamin K detection. Molecularly Imprinted Polymers (MIPs) could offer a solution, as they have been used as synthetic receptors in a large variety of biomimetic sensors for the detection of similar molecules over the past few decades, because of their robust nature and remarkable selectivity. In this article, the authors introduce a novel imprinting approach to create a MIP that is able to selectively rebind vitamin K 1. As the native structure of the vitamin does not allow for imprinting, an alternative imprinting strategy was developed, using the synthetic compound menadione (vitamin K 3) as a template. Target rebinding was analyzed by means of UV-visible (UV-VIS) spectroscopy and two custom-made thermal readout techniques. This analysis reveals that the MIP-based sensor reacts to an increasing concentration of both menadione and vitamin K 1. The Limit of Detection (LoD) for both compounds was established at 700 nM for the Heat Transfer Method (HTM), while the optimized readout approach, Thermal Wave Transport Analysis (TWTA), displayed an increased sensitivity with a LoD of 200 nM. The sensor seems to react to a lesser extent to Vitamin E, the analogue under study. To further demonstrate its potential application in biochemical research, the sensor was used to measure the absorption of vitamin K in blood serum after taking vitamin K supplements. By employing a gradual enrichment strategy, the sensor was able to detect the difference between baseline and peak absorption samples and was able to quantify the vitamin K concentration in good agreement with a validation experiment using High-Performance Liquid Chromatography (HPLC). In this way, the authors provide a first proof of principle for a low-cost, straightforward, and label-free vitamin K sensor

Label-free protein detection based on the heat-transfer method-a case study with the peanut allergen Ara h 1 and aptamer-based synthetic receptors

© 2015 American Chemical Society. Aptamers are an emerging class of molecules that, because of the development of the systematic evolution of ligands by exponential enrichment (SELEX) process, can recognize virtually every target ranging from ions, to proteins, and even whole cells. Although there are many techniques capable of detecting template molecules with aptamer-based systems with high specificity and selectivity, they lack the possibility of integrating them into a compact and portable biosensor setup. Therefore, we will present the heat-transfer method (HTM) as an interesting alternative because this offers detection in a fast and low-cost manner and has the possibility of performing experiments with a fully integrated device. This concept has been demonstrated for a variety of applications including DNA mutation analysis and screening of cancer cells. To the best our knowledge, this is the first report on HTM-based detection of proteins, in this case specifically with aptamer-type receptors. For proof-of-principle purposes, measurements will be performed with the peanut allergen Ara h 1 and results indicate detection limits in the lower nanomolar regime in buffer liquid. As a first proof-of-application, spiked Ara h 1 solutions will be studied in a food matrix of dissolved peanut butter. Reference experiments with the quartz-crystal microbalance will allow for an estimate of the areal density of aptamer molecules on the sensor-chip surface

Fingerprints for Structural Defects in Poly(thienylene vinylene) (PTV): A Joint Theoretical–Experimental NMR Study on Model Molecules

In the field of plastic electronics, low band gap conjugated polymers like poly(thienylene vinylene) (PTV) and its derivatives are a promising class of materials that can be obtained with high molecular weight via the so-called dithiocarbamate precursor route. We have performed a joint experimental- theoretical study of the full NMR chemical shift assignment in a series of thiophene-based model compounds, which aims at (i) benchmarking the quantum-chemical calculations against experiments, (ii) identifying the signature of possible structural defects that can appear during the polymerization of PTV's, namely head-to-head and tail-to-tail defects, and (iii) defining a criterion regarding regioregularity

Enantioselective ester cleavage of a-amino esters by Cu(II) complexes of chiral diamino alcols in acqueus surfactants solutions

A series of lipophilic ligands, 1-3, featuring an 1,2-ethylendiamino moiety as chelating subunit, one (1, 3) or two (2) chiral carbons, and an hydroxy function (except for 3) in the proximity of the coordination center, have been synthesized. Their Cu(II) complexes have been investigated as catalysts for the cleavage of p-nitrophenyl esters of phenylalanine (PhePNP) and phenylglycine (PhgPNP) in the presence of cationic aggregates formed by cetyltrimethylammonium bromide (CTABr) or ditetradecyldibutylammonium bromide (DMDBAB). Large rate accelerations (up to two order of magnitude) and quite remarkable enantioselectivities (from 11 to 35, as the ratios of the rate constants measured far me faster and slower reacting enantiomers) have been observed. In the case of ligands I the S-ligand complex reacts faster with the S-substrate and the enantioselectivity increases with the lipophilicity of the substituent of the chiral carbons. Using ligands 2, having two chiral centers, the most favoured situation is reached when all the chiral carbons of ligands and substrate have the same absolute configuration; in such a case, and using DMDBAB as cosurfactant enantioselectivities as high as 35 have been observed. The results are explained on the basis of a different reaction mechanism due to the compartmentalization of the reacting species (a ternary complex ligand/Cu(II)/substrate) in different loci of the aggregate. It is suggested that, depending on the hydrophobicity of the ternary complex, the effective nucleophile may switch from the Cu(II)-bound ligand's hydroxyl to a Cu(II) bound water molecule. The first mechanism is faster and prevails for the more lipophilic ternary complex