DNAzyme-Amplified Electrochemical Biosensor Coupled with pH Meter for Ca2+ Determination at Variable pH Environments

For more than 50% of multiparous cows, it is difficult to adapt to the sudden increase in calcium demand for milk production, which is highly likely to cause hypocalcemia. An electrochemical biosensor is a portable and efficient method to sense Ca2+ concentrations, but biomaterial is easily affected by the pH of the analyte solution. Here, an electrochemical biosensor was fabricated using a glassy carbon electrode (GCE) and single-walled carbon nanotube (SWNT), which amplified the impedance signal by changing the structure and length of the DNAzyme. Aiming at the interference of the pH, the electrochemical biosensor (GCE/SWNT/DNAzyme) was coupled with a pH meter to form an electrochemical device. It was used to collect data at different Ca2+ concentrations and pH values, and then was processed using different mathematical models, of which GPR showed higher detecting accuracy. After optimizing the detecting parameters, the electrochemical device could determine the Ca2+ concentration ranging from 5 μM to 25 mM, with a detection limit of 4.2 μM at pH values ranging from 4.0 to 7.5. Finally, the electrochemical device was used to determine the Ca2+ concentrations in different blood and milk samples, which can overcome the influence of the pH.

A Quantitative Study of Carmine Aqueous Solution Based on Drop-Coating Deposition Micro-Raman Spectroscopy (DCDR)

Carmine is a kind of colorant which is widely used in food, beverage, medicine, cosmetics and tobacco industry. However, excessive use of carmine may lead to the risks of carcinogenic, teratogenic and mutagenic, which seriously threaten the health and safety of consumers. In this paper, DCDR technology is utilized to develop a quantitative method for the detection of carmine, which requires only a small volume deposition of analyte solution (several μL) on a suitable hydrophobic substrate. The conventional Raman spectrum of carmine aqueous solution and corresponding Raman spectrum using DCDR method were compared, illustrating a much higher sensitivity for DCDR method. The Raman spectra of carmine aqueous solution with different concentrations of 100, 50, 10, 8, 4 and 2μg/mL are acquired from the spots on the “coffee-ring” with DCDR method. Using DCDR method, a good linear relationship has been observed between the intensities of the two characteristic peaks, 1364cm−1 as well as 1572cm−1, and the concentrations of the solution, with the linear correlation coefficient of R2>0.99. The results illustrate that DCDR method has a good potential in the quantitative analysis of colorant like carmine, providing a promising technique for a rapid detection for food additives.

Isolating Specific vs. Non-Specific Binding Responses in Conducting Polymer Biosensors for Bio-Fingerprinting

A longstanding challenge for accurate sensing of biomolecules such as proteins concerns specifically detecting a target analyte in a complex sample (e.g., food) without suffering from nonspecific binding or interactions from the target itself or other analytes present in the sample. Every sensor suffers from this fundamental drawback, which limits its sensitivity, specificity, and longevity. Existing efforts to improve signal-to-noise ratio involve introducing additional steps to reduce nonspecific binding, which increases the cost of the sensor. Conducting polymer-based chemiresistive biosensors can be mechanically flexible, are inexpensive, label-free, and capable of detecting specific biomolecules in complex samples without purification steps, making them very versatile. In this paper, a poly (3,4-ethylenedioxyphene) (PEDOT) and poly (3-thiopheneethanol) (3TE) interpenetrating network on polypropylene–cellulose fabric is used as a platform for a chemiresistive biosensor, and the specific and nonspecific binding events are studied using the Biotin/Avidin and Gliadin/G12-specific complementary binding pairs. We observed that specific binding between these pairs results in a negative ΔR with the addition of the analyte and this response increases with increasing analyte concentration. Nonspecific binding was found to have the opposite response, a positive ΔR upon the addition of analyte was seen in nonspecific binding cases. We further demonstrate the ability of the sensor to detect a targeted protein in a dual-protein analyte solution. The machine-learning classifier, random forest, predicted the presence of Biotin with 75% accuracy in dual-analyte solutions. This capability of distinguishing between specific and nonspecific binding can be a step towards solving the problem of false positives or false negatives to which all biosensors are susceptible.

Modification of a SERS-active Ag surface to promote adsorption of charged analytes: effect of Cu2+ ions

This work studies the impact of the electrostatic interaction between analyte molecules and silver nanoparticles (Ag NPs) on the intensity of surface-enhanced Raman scattering (SERS). For this, we fabricated nanostructured plasmonic films by immobilization of Ag NPs on glass plates and functionalized them by a set of differently charged hydrophilic thiols (sodium 2-mercaptoethyl sulfonate, mercaptopropionic acid, 2-mercaptoethanol, 2-(dimethylamino)ethanethiol hydrochloride, and thiocholine) to vary the surface charge of the SERS substrate. We used two oppositely charged porphyrins, cationic copper(II) tetrakis(4-N-methylpyridyl) porphine (CuTMpyP4) and anionic copper(II) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine (CuTSPP4), with equal charge value and similar structure as model analytes to probe the SERS signal. Our results indicate that the SERS spectrum intensity strongly, up to complete signal disappearance, correlates with the surface charge of the substrate, which tends to be negative. Using the data obtained and our model SERS system, we analyzed the modification of the Ag surface by different reagents (lithium chloride, polyethylenimine, polyhexamethylene guanidine, and multicharged metal ions). Finally, all those surface modifications were tested using a negatively charged oligonucleotide labeled with Black Hole Quencher dye. Only the addition of copper ions into the analyte solution yielded a good SERS signal. Considering the strong interaction of copper ions with the oligonucleotide molecules, we suppose that inversion of the analyte charge played a key role in this case, instead of a change of charge of the substrate surface. Changing the charge of analytes could be a promising way to get clear SERS spectra of negatively charged molecules on Ag SERS-active supports.

Determination of Lead Employing Simple Flow Injection AAS with Monolithic Alginate-Polyurethane Composite Packed In-Valve Column

A simple flow injection FlameAAS for lead determination with an alginate-polyurethane composite (ALG-PUC) monolithic in-valve column has been developed. The ALG-PUC monolithic rod was prepared by mixing methylene diphenyl diisocyanate with polyol and sodium alginate with the ratio of 2:1:1 by weight for a 5 min polymerization reaction. It was then put into a column (0.8 cm i.d × 11 cm length) situated in a switching valve for the FI set up. A single standard calibration could be obtained by plotting the loaded µg Pb2+ vs. FI response (absorbances). The loaded µg Pb2+ is calculated: μg Pb2+ = FRload × LT × CPb2+, where the FR load is the flow rate of the loading analyte solution (mL min−1), LT is the loading time (min), and CPb2+ is the Pb2+ concentration (µg mL−1). A linear calibration equation was obtained: FI response (absorbances) = 0.0018 [µg Pb2+] + 0.0032, R2 = 0.9927 for 1–150 µg Pb2+, and RSD of less than 20% was also obtained. Application of the developed procedure has been demonstrated in real samples.

Evaluation of Improved and Current Vanillin Based Colorimetric Quantification Methods of Triterpenoids

The most common colorimetric quantification method for triterpenoids utilizes vanillin in strongly acidic conditions to form a colored adduct with the analyte, and it has gained popularity because it is fast and easy to perform. Nevertheless, the detection range of this assay is limited and it is susceptible to side reactions, which cause an interference in the reading. Here, we quantify the rate of this interference in common solvents, and we present an alternative method to minimize the interference, which first incubates the analyte solution in perchloric acid at 60°C before the vanillin is added and finally quenched with acetic acid. We also successfully isolated the adduct that formed and confirmed that the color was due to vanillin polymerizing onto the analyte. The improved method had a correlation coefficient of 0.9959, as well as high accuracy and precision, which had a standard deviation of 0.072 mg/mL, and was not affected by minor changes in the conditions making it a robust method. Furthermore, our method had a limit of quantification of 2.37 mg/mL, which can analyze formulations with ease as well as a limit of detection of 0.782 mg/mL. Triterpenoids are quickly emerging as bioactive compounds, and as a result, our work improves upon current methods to quantify triterpenoids.

Flexible organic thin-film transistor immunosensor printed on a one-micron-thick film

Flexible and printed biosensor devices can be used in wearable and disposable sensing systems for the daily management of health conditions. Organic thin-film transistors (OTFTs) are promising candidates for constructing such systems. Moreover, the integration of organic electronic materials and biosensors is of extreme interest owing to their mechanical and chemical features. To this end, the molecular recognition chemistry-based design for the interface between sensor devices and analyte solution is crucial to obtain accurate and reproducible sensing signals of targets, though little consideration has been given to this standpoint in the field of device engineering. Here, we report a printed OTFT on a 1 μm-thick film functionalized with a sensing material. Importantly, the fabricated device quantitatively responds to the addition of a protein immunological marker. These results provide guidelines for the development of effective healthcare tools.

Application of drug–metal ion interaction principle in conductometric determination of imatinib, sorafenib, gefitinib and bosutinib

An analytical method for the quantification of anticancer agents such as imatinib, sorafenib, gefitinib and bosutinib using conductometry was developed. Each drug solution was mixed with measured concentration of metal ion (Cu2+) solution resulting in drug–metal ion complexation in the titration cell. Conductance was progressively decreased on addition of the analyte solution up to a point of maximum reduction, that is, the end point. Corrected conductance values were calculated from the observed conductance and used to plot a graph against the volume of drug solution added. No interferences were observed from blank and placebo as they gave no clear inflection in the conductivity during titration. The precision and the accuracy of the developed method was established by the analysis of quality control samples; %RSD of corrected conductance values <2% and recovery results within 100 ± 2% were achieved. The calibration graphs obtained were linear over the concentrations 1.0–1.4 mM for all the drugs (R2 > 0.99). The drugs were successfully analyzed in their respective dosage forms prepared in-house. The method has offered easier, faster and cost-effective analysis of the selected drugs and can be used for routine determinations in the quality control laboratories. More importantly, it is an environmental friendly procedure, as no organic solvent was used throughout the analysis.