Alternative method for rhamnolipids quantification using an electrochemical platform based on reduced graphene oxide, manganese nanoparticles and molecularly imprinted Poly(L-Ser).

Rhamnolipids (RHLs) are promising biosurfactants with important applications in several industrial segments. These compounds are produced through biotechnological processes using the bacteria Pseudomonas Aeruginosa. The main methods of analyzing this compound are based on chromatographic techniques. In this study, an electrochemical sensor based on a platform modified with reduced graphene oxide, manganese nanoparticles covered with a molecularly imprinted poly (L-Ser) film was used as an alternative method to quantify RHL through its hydrolysis product, acid 3-hydroxydecanoic acid (3-HDA). The proposed sensor was characterized microscopically, spectroscopically and electrochemically. Under optimized experimental conditions, an analytical curve was obtained in the linear concentration range from 2.0 × 10-12 mol L-1 to 1.0 × 10-10 mol L-1. The values estimated of LOD, LOQ and AS were 8.3 × 10-13 mol L-1, 2.7 × 10-12 mol L-1and 1.3 × 107 A L mol-1, respectively. GCE/rGO/MnNPs/L-Ser@MIP exhibits excellent selectivity, repeatability, and high stability for the detection of 3-HDA. Furthermore, the developed method was successfully applied to the recognition of the hydrolysis product (3-HDA) of RHLs obtained from guava agro-waste. Statistical comparison between GCE/rGO/MnNPs/L-Ser@MIP and HPLC method confirms the accuracy of the electrochemical sensor within a 95% confidence interval.

Using a disposable platform based on reduced graphene oxide, iron nanoparticles and molecularly imprinted polymer for voltammetric determination of vanillic acid in fruit peels.

This work reports the development and application of a disposable electrochemical platform for vanillic acid (VA) detection using screen-printed electrode modified with reduced graphene oxide, iron nanoparticles and molecularly imprinted poly(pyrrole) film. The electrochemical platform was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Using optimized conditions, the proposed disposable platform presented linear concentration ranges of 1.0 × 10-9 to 1.5 × 10-7 mol/L. The limits of detection and quantification obtained for the device were 3.1 × 10-10 and 1.0 × 10-9 mol/L, respectively. The electrochemical platform was found to be selective for VA recognition and presented voltammetric responses with good repeatability and stability. The analytical methodology developed was applied for VA determination in banana and orange peels. The results obtained showed that the proposed electrochemical platform has a good accuracy when applied for the determination of VA.

Fructose determination in fruit juices using an electrosynthesized molecularly imprinted polymer on reduced graphene oxide modified electrode.

The present work reports the development of a novel electrochemical sensor for the selective detection of fructose. The sensor was developed through electropolymerization of a molecularly imprinted polymer film on a reduced graphene oxide modified electrode. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, atomic force microscopy and RAMAN spectroscopy. Through the application of the modified electrode, the recognition of fructose molecules occurred in a concentration range of 1.0 × 10-14 to 1.0 × 10-11 mol L-1, under a Langmuir adsorption isothermal model. The sensitivity and limits of detection and quantification obtained for the sensor were 9.9 × 107 A L mol-1, 3.2 × 10-15 mol L-1 and 1.1 × 10-14 mol L-1, respectively. The analytical method used for the detection of fructose presented good reproducibility, stability and accuracy, and was successfully applied for the quantification of this sugar in orange, apple and grape juices.

Non-enzymatic lactose molecularly imprinted sensor based on disposable graphite paper electrode.

Lactose (LAC) is a disaccharide - major sugar, present in milk and dairy products. LAC content is an important indicator of milk quality and abnormalities in food industries, as well as in human and animal health. The present study reports the development of an innovative imprinted voltammetric sensor for sensitive detection of LAC. The sensor was constructed using electropolymerized pyrrole (Py) molecularly imprinted polymer (MIP) on graphite paper electrode (PE). The MIP film was constructed through the electrosynthesis of polypyrrole (PPy) in the presence of LAC (template molecule) on PE (PPy/PE). To optimize the detection conditions, several factors affecting the PPy/PE sensor performance were assessed by multivariate methods (Plackett-Burman design and central composite design). Under optimized conditions, the proposed analytical method was applied for LAC detection in whole and LAC-free milks, where it demonstrated high sensitivity and selectivity, with two dynamic linear ranges of concentration (1.0-10 nmol L-1 and 25-125 nmol L-1) and a detection limit of 0.88 nmol L-1. The MIP sensor showed selective molecular recognition for LAC in the presence of structurally related molecules. The proposed PPy/PE sensor exhibited good stability, as well as excellent reproducibility and repeatability. Based on the results obtained, the PPy/PE is found to be highly promising for sensitive detection of LAC.

Electrochemical sensor based on reduced graphene oxide and molecularly imprinted poly(phenol) for d-xylose determination.

The present work reports the development of an electrochemical sensor based on molecularly imprinted polymer for the determination of d-xylose. This is the first report of its kind in the literature. The sensor was prepared through the modification of a glassy carbon electrode with reduced graphene oxide and molecularly imprinted poly(phenol) film. The use of graphene oxide and molecularly imprinted poly(phenol) film led to remarkable improvements in the sensor sensitivity and selectivity, respectively. The electrode was characterized by several techniques, including cyclic voltammetry, differential pulse voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, atomic force microscopy and RAMAN spectroscopy. The proposed sensor presented linear responses ranging from 1.0 × 10-13 to 1.0 × 10-11 mol L-1. The amperometric sensitivity, limit of detection, and limit of quantification obtained were 6.7 × 105 A L mol-1; 8.0 × 10-14 mol L-1 and 2.7 × 10-13 mol L-1 (n = 3), respectively. The proposed analytical method was successfully applied in sugarcane bagasse, which is known to contain large amounts of d-xylose and other structurally similar molecules in its composition. The chemical composition of sugarcane bagasse makes this biomass suitable for evaluating the ability of the sensor to specifically detect the target molecule. Mean recoveries obtained in the analysis ranged from 95.4 to 105.0%; this indicates that the proposed method has good accuracy when applied toward the determination of d-xylose.