Molecularly imprinted electrochemical sensor, formed on Ag screen-printed electrodes, for the enantioselective recognition of d and l phenylalanine

Dual-Photoelectrode Fuel Cell Based Self-Powered Sensor for a Picomole Level Pollutant: Using an In Situ Molecularly Imprinted p-Type Organic Photocathode

Developing a dual-photoelectrode fuel cell based self-powered sensor (DPFC-SPS) with an ideal signal output capability and high sensitivity performance for the detection of environmental pollutant atrazine (ATZ) has an important value. In this work, the in situ molecularly imprinting functionalized p-type organic semiconductor polyterthiophene (MI-pTTh) is used as a photocathode to construct a DPFC-SPS toward the typical environmental pollutant ATZ for the first time. Due to its excellent photoactivity, higher stability, and superior oxygen reduction reaction activity, pTTh serves as the photocathode material for constructing a self-powered sensing platform with a stable signal output and high photoelectric activity. Based on the sensitive light-triggered large self-bias of the DPFC-SPS, the open circuit potential (EOCV) of the device reaches 1.21 V and the maximum power density (Pmax) reaches 121.5 μW·cm-2, which is much higher than most reported PFC-SPSs. Simultaneously, in situ molecularly imprinted (MI) functionization of pTTh can further endow it with specific recognition ability, helping the constructed SPS achieve high sensitivity, selectivity, and effective recognition of the important environmental pollutants ATZ in complex systems. It exhibits a broad linear relationship from 0.002 to 100 nM and a low detection limit (estimated by S/N > 3) of 0.21 pM toward ATZ. The mechanism of the binding kinetics of the MI-pTTh with the target ATZ is further studied via in situ infrared spectroscopy. This work provides theoretical guidance for sensing strategies using dual-photoelectrode devices and offers a rational device design for cost-effective electricity generation from renewable resources.

Construction of an enzyme-based all-fiber SPR biosensor for detection of enantiomers

Chiral analysis of amino acids (AAs) is of great importance in medical science due to the distinctive effect of AA isomers on human health. Although various chiral recognition techniques have been developed, the quantitative chiral recognition of low-level AA isomers remains challenging. Here, we combined the fiber optic SPR with an enzyme-substrate recognition mechanism to construct a direct-assay-type chiral AA biosensor. As a proof-of-concept attempt, a recently discovered Rasamsonia emersonii D-amino acid oxidase (ReDAAO) with a wide substrate spectrum and high stability was immobilized on the graphene oxide and gold nanorods composites (GO-AuNRs), using both EDC/NHS coupling and the gold-binding peptide (GBP) method. Such a biosensor can distinguish two AA isomers at the same concentration. It achieved specific detection of D-amino acids (D-AAs) with a linear range from 5x10^-4 mM to 30 mM. Furthermore, it showed good resistance to enantiomeric interference. When the percentage of D-AA increases in the isomer mixture, a good linear relationship between the D/(D + L)-AA ratio and SPR spectral shift was obtained. This unique combination of the enzyme, nanocomposite, and SPR taps into the rich reservoir of proteins for chiral receptors. It lays the foundation for protein-based chiral recognition of other clinically important small molecules in future biosensor designs.

Voltammetric Determination of Phenylalanine Using Chemically Modified Screen-Printed Based Sensors

This paper describes the sensitive properties of screen-printed carbon electrodes (SPCE) modified by using three different electroactive chemical compounds: Meldola’s Blue, Cobalt Phthalocyanine and Prussian Blue, respectively. It was demonstrated that the Prussian Blue (PB) modified SPCE presented electrochemical signals with the highest performances in terms of electrochemical process kinetics and sensitivity in all the solutions analyzed. PB-SPCE was demonstrated to detect Phe through the influence it exerts on the redox processes of PB. The PB-SPCE calibration have shown a linearity range of 0.33–14.5 µM, a detection limit (LOD) of 1.23 × 10−8 M and the standard deviation relative to 3%. The PB-SPCE sensor was used to determine Phe by means of calibration and standard addition techniques on pure samples, on simple pharmaceutical samples or on multicomponent pharmaceutical samples. Direct determination of the concentration of 4 × 10−6–5 × 10−5 M Phe in KCl solution showed that the analytical recovery falls in the range of 99.75–100.28%, and relative standard deviations in the range of 2.28–3.02%. The sensors were successfully applied to determine the Phe in pharmaceuticals. The validation of the method was performed by using the FTIR, and by comparing the results obtained by PB-SPCE in the analysis of three pharmaceutical products of different concentrations with those indicated by the producer.

A robust composite hydrogel consisting of polypyrrole and β-cyclodextrin-based supramolecular complex for the label-free amperometric immunodetection of motilin with well-defined dual signal response and high sensitivity

The label-free amperometric immunosensor is a simple, convenient and reliable method for the detection of diseases markers. Its performance heavily relies on the properties of the sensing substrate. In this paper, we proposed a robust composite hydrogel that consists of polypyrrole and vinyl ferrocene/mono-aldehyde β-cyclodextrin (β-CD) complex as a sensing and immobilizing substrate. Surprisingly, it was observed that the microstructure of the hybrid hydrogel could be well regulated by the feed ratio of vinylferrocene and so are the electrochemical properties. Depending on the dual electrochemical active compositions, a large loading capacity of antibodies and meanwhile the excellent conductivity, the square wave voltammetry results of the optimized immunosensor for the detection of motilin exhibited a well-defined dual signal response, with a wide linear range both from 10 pg mL-1 to 100 ng mL-1 for motilin, and an ultralow limit of detection of 6.29 pg mL-1 and 2.73 pg mL-1. More importantly, the immunosensor exhibited an especially sensitive response with the slope value as high as 31.342 and 25.751 respectively, which makes great sense in the practical diagnosis.

Effect of surface functionality of molecularly imprinted composite nanospheres on specific recognition of proteins

The surface functionality of biomaterial plays a primary role in determining its application in biorecognition and drug delivery. In our work, three types of synthetic tailoring polymer nanospheres with hierarchical architecture were constructed to obtain functional polymer layer with disparate chemical motifs for protein adsorption via surface imprinting and grafting copolymerization. In this polymerization system, the structure stability of template protein bovine serum albumin (BSA) is well maintained within a certain range, which facilitated the accurate imprinting and precise identification. A comprehensive protocol for screening different functional layer is proposed through comparing the adsorption behavior, selectivity, identification and responsiveness to medium pH of three functional layers. Our study demonstrates that surface functionality greatly influences the adsorption capacity and selectivity of adsorption material. The functional layer with ionic liquid structure that could only provide multiple non-covalent binding sites is beneficial to the proteins aggregation and extraction, while the anti-nonspecific binding functional layer of biomaterial with zwitterionic structure for specific protein capture is promising to serve as a preferable antigen-antibody communication network, which shows great potential for protein recognition and separation. In summary, our proposed strategy provides a systematic selection criterion of biomaterials for effective application in biosensors.

A Review on Electrochemical Sensors and Biosensors Used in Phenylalanine Electroanalysis

Phenylalanine is an amino acid found in breast milk and in many foods, being an essential nutrient. This amino acid is very important for the human body because it is transformed into tyrosine and, subsequently, into catecholamine neurotransmitters. However, there are individuals who were born with a genetic disorder called phenylketonuria. The accumulation of phenylalanine and of some metabolites in the body is dangerous and may cause convulsions, brain damage and mental retardation. Determining the concentration of phenylalanine in different biologic fluids is very important because it can provide information about the health status of the individuals envisaged. Since such determinations may be made by using electrochemical sensors and biosensors, numerous researchers have developed such sensors for phenylalanine detection and different sensitive materials were used in order to improve the selectivity, sensitivity and detection limit. The present review aims at presenting the design and performance of some electrochemical bio (sensors) traditionally used for phenylalanine detection as reported in a series of relevant scientific papers published in the last decade.

β-Cyclodextrin-Immobilized Ni/Graphene Electrode for Electrochemical Enantiorecognition of Phenylalanine

In this work, a Ni/graphene (Ni/G) electrode was designed and fabricated by plasma-enhanced chemical vapor deposition (PECVD) for the ultrasensitive recognition of d- and l-phenylalanine. Through a single-step PECVD process, the Ni/G electrode can achieve better hydrophilicity and larger catalytic surface area, which is beneficial for the electrochemical recognition of bio-objects. After surface modification with β-cyclodextrin, the Ni/G electrode can distinguish d-phenylalanine from l-phenylalanine according to a 0.09 V peak shift in differential pulse voltammetry tests. Moreover, this Ni/G electrode achieved a detection limit as low as 1 nM and a wide linear range from 1 nM to 10 mM toward l-phenylalanine, with great storage stability and working stability.

Single-Template Molecularly Imprinted Chiral Sensor for Simultaneous Recognition of Alanine and Tyrosine Enantiomers

Chiral recognition of l-amino acids is of significant importance due to the crucial role of l-amino acids in life sciences and pharmaceutics. In this work, a chiral sensor with capability of probing two chiral amino acids by an attractive single-template molecular imprinting strategy is introduced and used in the simultaneous chiral recognition of d/l-alanine (d/l-Ala) and d/l-tyrosine (d/l-Tyr). The assay relies on the hydrolysis of l-alanyl-l-tyrosine dipeptide doped in silica/polypyrrole (SiO₂/PPy) under acidic conditions, resulting in l-Ala and l-Tyr coimprinted chiral sensor. This work opens up a new avenue for simultaneous chiral sensing of two or more chiral amino acids by incorporating only one template, circumventing the shortcomings encountered with multitemplate molecularly imprinted technology.

Highly sensitive and selective "off-on" fluorescent sensing platform for ClO- in water based on silicon quantum dots coupled with nanosilver

We present a new "off-on" fluorescence probe for detecting hypochlorite (ClO^-) based on silicon quantum dots coupled with silver nanoparticles (SiQDs/AgNPs) as nanocomplexes. Via introducing N-[3-(trimethoxysilyl)propyl]ethylenediamine and catechol as initial reactants, silicon quantum dots (SiQDs) with excellent properties were synthesized through a simple hydrothermal method. Transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of quantum dots. The fluorescence of SiQDs could be quenched by the silver nanoparticles (AgNPs) by surface plasmon-enhanced energy transfer (SPEET) from SiQDs (donor) to AgNPs (acceptor). The AgNPs could be etched by adding ClO^-, thus freeing the SiQDs from the AgNP surfaces and restoring the SiQDs' fluorescence. The sensing system exhibits many advantages, such as wide linear response range, high sensitivity, and excellent selectivity. Under optimized conditions, wide linear ranges (from 0.1 to 100.0 μM) and low detection limits (0.08 μM) were obtained for ClO^-. Graphical Abstract.

Electrochemical Enantiomer Recognition Based on sp³-to-sp² Converted Regenerative Graphene/Diamond Electrode

It is of great significance to distinguish enantiomers due to their different, even completely opposite biological, physiological and pharmacological activities compared to those with different stereochemistry. A sp³-to-sp² converted highly stable and regenerative graphene/diamond electrode (G/D) was proposed as an enantiomer recognition platform after a simple β-cyclodextrin (β-CD) drop casting process. The proposed enantiomer recognition sensor has been successfully used for d and l-phenylalanine recognition. In addition, the G/D electrode can be simply regenerated by half-minute sonication due to the strong interfacial bonding between graphene and diamond. Therefore, the proposed G/D electrode showed significant potential as a reusable sensing platform for enantiomer recognition.