Feasible electrochemical biosensor based on plasma polymerization-assisted composite of polyacrylic acid and hollow TiO2 spheres for sensitively detecting lysozyme

Electrochemical and thermal detection of allergenic substance lysozyme with molecularly imprinted nanoparticles

Lysozyme (LYZ) is a small cationic protein which is widely used for medical treatment and in the food industry to act as an anti-bacterial agent; however, it can trigger allergic reactions. In this study, high-affinity molecularly imprinted nanoparticles (nanoMIPs) were synthesized for LYZ using a solid-phase approach. The produced nanoMIPs were electrografted to screen-printed electrodes (SPEs), disposable electrodes with high commercial potential, to enable electrochemical and thermal sensing. Electrochemical impedance spectroscopy (EIS) facilitated fast measurement (5-10 min) and is able to determine trace levels of LYZ (pM) and can discriminate between LYZ and structurally similar proteins (bovine serum albumin, troponin-I). In tandem, thermal analysis was conducted with the heat transfer method (HTM), which is based on monitoring the heat transfer resistance at the solid-liquid interface of the functionalized SPE. HTM as detection technique guaranteed trace-level (fM) detection of LYZ but needed longer analysis time compared to EIS measurement (30 min vs 5-10 min). Considering the versatility of the nanoMIPs which can be adapted to virtually any target of interest, these low-cost point-of-care sensors hold great potential to improve food safety.

Polyacrylic Acid Nanoplatforms: Antimicrobial, Tissue Engineering, and Cancer Theranostic Applications

Polyacrylic acid (PAA) is a non-toxic, biocompatible, and biodegradable polymer that gained lots of interest in recent years. PAA nano-derivatives can be obtained by chemical modification of carboxyl groups with superior chemical properties in comparison to unmodified PAA. For example, nano-particles produced from PAA derivatives can be used to deliver drugs due to their stability and biocompatibility. PAA and its nanoconjugates could also be regarded as stimuli-responsive platforms that make them ideal for drug delivery and antimicrobial applications. These properties make PAA a good candidate for conventional and novel drug carrier systems. Here, we started with synthesis approaches, structure characteristics, and other architectures of PAA nanoplatforms. Then, different conjugations of PAA/nanostructures and their potential in various fields of nanomedicine such as antimicrobial, anticancer, imaging, biosensor, and tissue engineering were discussed. Finally, biocompatibility and challenges of PAA nanoplatforms were highlighted. This review will provide fundamental knowledge and current information connected to the PAA nanoplatforms and their applications in biological fields for a broad audience of researchers, engineers, and newcomers. In this light, PAA nanoplatforms could have great potential for the research and development of new nano vaccines and nano drugs in the future.

Nitrogen-doped Carbon@TiO2 double-shelled hollow spheres as electrochemical sensor for simultaneous determination of dopamine and paracetamol in human serum and saliva

As the most commonly used antipyretic and analgesic drug, paracetamol (PA) coexists with neurotransmitter dopamine (DA) in real biological samples. Their simultaneous determination is extremely important for human health, but they also interfere with each other. In order to improve the conductivity, adsorption affinity, sensitivity, and selectivity of TiO₂-based electrochemical sensor, N-doped carbon@TiO₂ double-shelled hollow sphere (H–C/N@TiO₂) is designed and synthesized by simple alcoholic and hydrothermal method, using polystyrene sphere (PS) as a template. Meanwhile, TiO₂ hollow spheres (H–TiO₂) or N-doped carbon hollow spheres (H–C/N) are also prepared by the same method. H–C/N@TiO₂ has good conductivity, charge separation, and the highly enhanced and stable current responses for the detection of PA and DA. The detection limit and linear range are 50.0 nmol/L and 0.3–50 μmol/L for PA, 40.0 nmol/L and 0.3–50 μmol/L for DA, respectively, which are better than those of carbon-based sensors. Moreover, this electrochemical sensor, with high selectivity, strong anti-interference, high reliability, and long time durability, can be used for the simultaneous detection of PA and DA in human blood serum and saliva. The high electrochemical performance of H–C/N@TiO₂ is attributed to the multi-functional combination of different layers, because of good conductivity, absorption and electrons transfer ability from in-situ N-doped carbon and electrocatalytic activity from TiO₂.

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Nitrogen-doped carbon@TiO₂ double-shelled hollow spheres are constructed.

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Double-shelled hollow spheres bring more heterojunctions interface and multi-active sites.

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Paracetamol and dopamine are simultaneously determined by electrochemical sensor.

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Synergistic effect of N-doped carbon, TiO₂ and double-shelled structure are observed.

A simple method to construct a low-cost immunosensor based on a dithiol-functionalized polydopamine platform

A simple and low-cost electrochemical CEA immunosensor was investigated via the self-polymerization of dopamine and a dithiol compound spacer for the covalent immobilization of antibodies. The designed CEA immunosensor exhibited a linear response and a low detection limit.

Porphyrin-based covalent organic framework as bioplatfrom for detection of vascular endothelial growth factor 165 through fluorescence resonance energy transfer

A fluorescent aptasensor based on porphyrin-based covalent organic framework (p-COF) and carbon dots (CDs) was constructed for detecting vascular endothelial growth factor 165 (VEGF₁₆₅) and for imaging of the breast cancer cell line Michigan cancer foundation-7 (MCF-7). CDs synthesized with strong photoluminescence at λ∼380 nm were used as donors to label the VEGF₁₆₅-targeted aptamers (Apt_VEGF/CDs). Additionally, the p-COF nanostructure comprised rich functional groups of CN on the surface and π-stacking planar nanostructure, resulting in the CDs adsorption via weakly π-π stacking, hydrogen bond and the Van der Waals force. Thereby, the fluorescence resonance energy transfer (FRET) occurred due to the close distance between the p-COF network and CDs, leading to the quenching of the fluorescence feature of CDs and p-COF. In the presence of VEGF₁₆₅, the G-quadruplex was formed via the specific binding between VEGF₁₆₅ and aptamer. It impelled that the release of partial VEGF₁₆₅-Apt_VEGF/CDs complex, affording the fluorescence recovery of the sensing system to some extent. Consequently, the proposed Apt_VEGF/CDs/p-COF fluorescence biosensor offered excellent analytical performances for the VEGF₁₆₅ detection, displaying a detection limit of 20.9 fg mL^-1 within a wide linear range of the VEGF₁₆₅ concentration of 1.0 pg mL^-1-100 ng mL^-1. The developed fluorescence biosensor was also used to determine VEGF₁₆₅-overexpressed in MCF-7 cancer cells. Thereby, the present work can greatly widen the application of COFs in the development of aptasensors and cancer diagnosis.

Impedimetric Aptamer-Based Biosensors: Applications

Impedimetric aptamer-based biosensors show high potential for handheld devices and point-of-care tests. In this review, we report on recent advances in aptamer-based impedimetric biosensors for applications in biotechnology. We detail on analytes relevant in medical and environmental biotechnology as well as food control, for which aptamer-based impedimetric biosensors were developed. The reviewed biosensors are examined for their performance, including sensitivity, selectivity, response time, and real sample validation. Additionally, the benefits and challenges of impedimetric aptasensors are summarized.

Graphene oxide as a cartridge enable on-line assembly of photosensitizer for 1O2-based electrochemical aptasensing

An ultrasensitive ¹O₂-based electrochemical aptasensor by on-line assembly of photosensitizers using graphene oxide (GO) as a cartridge is reported. In the presence of target protein lysozyme, the interaction of lysozyme with aptamer led to the dissociation of dsDNA and release of the aptamer-lysozyme complex to solution, with DNA-c retaining on the electrode; then, the photosensitizer phloxine B (PB) was assembled on the electrode since GO can simultaneously adsorb DNA-c and PB molecules. Upon irradiation by a green LED, ¹O₂ was generated by photocatalysis of PB molecules and then cleaved the DNA-c, leading to remarkably decreased impedance signals that linearly respond with the logarithm of lysozyme concentration. Benefitting from the efficient photosensitization ability of PB and the high PB-loading capacity of GO, the developed sensor allowed determination of 0.001 to 100 nM lysozyme with a limit of detection of about 0.14 pM. The relative standard deviation (RSD) for five independent electrodes with 1 nM lysozyme was 3.1%, indicating satisfactory reproducibility. The sensor also showed excellent selectivity toward lysozyme in the presence of interfering substances and was applied to the determination of lysozyme in urine samples with recoveries ranging from 91 to 101%. The on-line assembly of photosensitizer technique opens a new way for amplified electrosensing of biomolecules. Graphical abstract An on-line assembly of photosensitizers and DNA on electrode was developed using graphene oxide a cartridge and the photocatalytic electrosensor can be used for label-free detection of lysozyme as low as 1 pM.

A chemiluminescence assay for determination of lysozyme based on the use of magnetic alginate-aptamer composition and hemin@HKUST-1

Lysozyme aptamer-functionalized magnetic alginate hydrogel was prepared for separation and enrichment of lysozyme. Luminol-labeled aptamer was used as a signal tag, and the signal tag was adsorbed on magnetic carboxylated carbon nanotubes based on the π-interaction. When lysozyme was added, the aptamer specifically binds to the lysozyme, causing the signal tag to detach from the magnetic carboxylated carbon nanotubes. When the aptamer/lysozyme complex bound to the complementary single strand of aptamer on the hemin@HKUST-1, lysozyme was released. The released lysozyme can be recombined with the signal tag adsorbed on the magnetic carboxylated carbon nanotube, allowing more signal tag to be dispersed into the solution. Determination of lysozyme was achieved by releasing the luminol-labeled aptamer to generate a chemiluminescence signal at a wavelength of 425 nm. It was proved by experiments that the synthesized hemin@HKUST-1 had a strong catalytic effect on the luminol-NaOH-H₂O₂ system. The chemiluminescence signal was increased nearly 100 times. The complementary pairing allowed the luminol to be immobilized on the surface of hemin@HKUST-1. The generation and consumption of short-lived reactive oxygen species were concentrated on the surface of the MOFs, which improves the chemiluminescence efficiency. The introduction of hemin@HKUST-1 and DNA solved the defects of chemiluminescence analysis. The chemiluminescence assay was able to detect lysozyme with linear range of 1.05 × 10^-6 U∙mg^-1 (6.00 × 10^-13 mol∙L^-1)-1.25 × 10^-2 U∙mg^-1 (7.14 × 10^-9 mol∙L^-1); the detection limit was 3.50 × 10^-7 U∙mg^-1 (2.00 × 10^-13 mol∙L^-1) (R² = 0.99). The recovery of lysozyme in spiked saliva samples was 97.4-102.8%. Graphical abstract Schematic presentation of chemiluminescence assay. Lysozyme (Lys) was captured by aptamer-modified magnetic sodium alginate (M-Alg-Apt); Glycine (pH = 2) as eluent for Lys. Luminol-modified Apt (Apt-luminol) as signal tag; magnetic carbon nanotubes (MCNTs) as adsorption matrix; cDNA was complementary to Apt; hemin@HKUST-1 as catalyst.

A chemiluminescence biosensor for lysozyme detection based on aptamers and hemin/G-quadruplex DNAzyme modified sandwich-rod carbon fiber composite

In our work, aptamers and hemin/G-quadruplex DNAzyme modified sandwich-rod graphene quantum dots @ graphene oxide @ carbon fiber composite (DNAzyme/L-Apt/GQDs@GO@CF) was successfully prepared for sensitive and selective chemiluminescence (CL) detection of lysozyme (LZM). Initially, GQDs@GO@CF was successfully prepared and characterized. Lysozyme aptamers (L-Apt) as a recognition element and hemin/G-quadruplex DNAzyme (DNAzyme) as a catalyst of luminal - H₂O₂ were modified on the surface of GQDs@GO@CF, sequentially. The immobilization properties of GQDs@GO@CF to L-Apt and the adsorption properties of L-Apt/GQDs@GO@CF to DNAzyme were also researched, respectively. Then, the modified sandwich-rod carbon fiber composite was applied to the construction of CL biosensor for LZM detection. When LZM existed, DNAzyme would be released from the surface of L-Apt/GQDs@GO@CF and catalyzed the reaction of luminal - H₂O₂. Under optimized conditions, the CL biosensor for LZM detection showed wide linear range of 2.64 × 10^-10 to 6.6 × 10^-8 g/L and low detection limit of 1.25 × 10^-11 g/L (3δ). Finally, the CL biosensor was successfully used for LZM detection in human urine samples and illustrated the potential application in pratical samples.

Electrogenerated chemiluminescence aptasensor for lysozyme based on copolymer nanospheres encapsulated black phosphorus quantum dots

Black phosphorus quantum dots (BPQDs) can react with Ru(bpy)₃²⁺ to generate strong anodic electrogenerated chemiluminescence (ECL). However, the instability and the lack of functional groups on BPQDs limit its further application in the fabrication of ECL biosensor. In the present work, uniform BPQDs-styrene-acrylamide (St-AAm) nanospheres (BSAN) are synthesized by encapsulating BPQDs into St-AAm copolymer nanospheres. Sufficient amount of BPQDs can be embedded into nanospheres, and react with Ru(bpy)₃²⁺ to generate strong anodic ECL which is comparable to that of pure BPQDs. Amino group of polymer endows BPQDs the ability to connect with DNA, and can be used to fabricate ECL aptasensor for the sensitive detection of lysozyme. The proposed aptasensor shows high sensitivity, good selectivity and stability for the detection of lysozyme in the range of 0.1-100 pg mL^-1 with a detection limit of 0.029 pg mL^-1 (3σ). The proposed method reveals the promising ECL sensing application of BP nanomaterials in the detection of various proteins.

Electrochemical performance of myoglobin based on TiO2-doped carbon nanofiber decorated electrode and its applications in biosensing

A new biosensing strategy based on a TiO₂-doped carbon nanofiber (CNF) composite modified electrode was developed. TiO₂@CNF was prepared by electrospinning with further carbonization, before being characterized by various methods and used for electrode modification on the surface of carbon ionic liquid electrode (CILE). Myoglobin (Mb) was further immobilized on the modified electrode surface. The results of ultraviolet-visible (UV-vis) and Fourier transform infrared (FT-IR) spectroscopy showed that Mb maintained its native structure without denaturation in the composite film. Direct electron transfer and the electrocatalytic properties of Mb on the electrode surface were further investigated. A pair of quasi-reversible redox peaks appeared on the cyclic voltammogram, indicating that direct electrochemistry of Mb was realized in the nanocomposite film. This could be attributed to the specific properties of TiO₂@CNF nanocomposite, including a large surface-to-volume ratio, good biocompatibility and high conductivity. Nafion/Mb/TiO₂@CNF/CILE exhibited an excellent electrochemical catalytic ability in the reduction of trichloroacetic acid, NaNO₂ and H₂O₂. All results demonstrated potential applications of TiO₂@CNF in third-generation electrochemical biosensors.

A new biosensing strategy based on a TiO₂-doped carbon nanofiber (CNF) composite modified electrode was developed.

A facile electrochemical aptasensor for lysozyme detection based on target-induced turn-off of photosensitization

The quantification of proteins is essential in fundamental research or clinical applications. Here, we developed a facile electrochemical aptasensor based on target-induced turn-off of photosensitization for label-free and ultrasensitive detection of protein (exemplified by lysozyme). EB (ethidium bromide) molecules that were embedded in dsDNA between lysozyme binding aptamer and complementary DNA immobilized on the electrode, could photo-cleave the dsDNA via singlet oxygen (O₂¹) during photosensitization, resulting in a high voltammetry current of the [Fe(CN)₆]^3-/4-. Upon recognition of the lysozyme by aptamer, the EB molecules were released from dsDNA, and its photosensitization activity was turned off. As a result, more amount of complementary DNA was retained on the Au nanoparticles modified carbon nanotube paste electrode (AuNPs-CNPE), leading to a declined voltammetry current. Such a sensing strategy allowed detection of 10 pM-1 µM lysozyme with a low detection limit (about 2 pM). Besides, the sensor was free of labeling procedure as well as extra signal amplification step, and the CNPE modification was quite simple, only with AuNPs. The sensor also showed excellent selectivity toward lysozyme in the presence of interfering proteins, such as thrombin, bovine serum albumin, myoglobin, etc. The proposed sensor was applied to the determination of lysozyme in urine samples with the recoveries ranging from 96.6% to 101%. The proposed biosensor holds a great promise in developing other electrochemical sensors based on photosensitization.

CdTe/CdSe quantum dot-based fluorescent aptasensor with hemin/G-quadruplex DNzyme for sensitive detection of lysozyme using rolling circle amplification and strand hybridization

Lysozyme with a small monomeric globular enzymatic protein is part of the innate immune system, and its deficiency can cause the increased incidence of disease. Herein, we devise a new signal-enhanced fluorescence aptasensing platform for quantitative screening of lysozyme by coupling with rolling circle amplification (RCA) and strand hybridization reaction, accompanying the assembly of CdTe/CdSe quantum dots (QDs) and hemin/G-quadruplex DNzyme. Initially, target-triggered release of the primer was carried out from DNA duplex via the reaction of the aptamer with the analyte, and the released primer could be then utilized as the template to produce numerous repeated oligonucleotide sequences by the RCA reaction. Following that, the formed long-stranded DNA simultaneously hybridized with the CdTe/CdSe QD-labeled probe and hemin/G-quadruplex DNzyme strand in the system, thereby resulting in the quenching of QD fluorescent signal through the proximity hemin/G-quadruplex DNzyme on the basis of transferring photoexcited conduction band electrons of quantum dots to Fe(III)/Fe(II)-protoporphyrin IX (hemin) complex. Under optimal conditions, the fluorescent signal decreased with the increasing target lysozyme within the dynamic range from 5.0 to 500nM with a detection limit (LOD) of 2.6nM at the 3s_blank criterion. Intra-assay and interassay coefficients of variation (CVs) were below 8.5% and 11.5%, respectively. Finally, the system was applied to analyze spiked human serum samples, and the recoveries in all cases were 85-111.9%.

Free-Radical-Induced Grafting from Plasma Polymer Surfaces

With the advances in science and engineering in the second part of the 20th century, emerging plasma-based technologies continuously find increasing applications in the domain of polymer chemistry, among others. Plasma technologies are predominantly used in two different ways: for the treatment of polymer substrates by a reactive or inert gas aiming at a specific surface functionalization or for the synthesis of a plasma polymer with a unique set of properties from an organic or mixed organic-inorganic precursor. Plasma polymer films (PPFs), often deposited by plasma-enhanced chemical vapor deposition (PECVD), currently attract a great deal of attention. Such films are widely used in various fields for the coating of solid substrates, including membranes, semiconductors, metals, textiles, and polymers, because of a combination of interesting properties such as excellent adhesion, highly cross-linked structures, and the possibility of tuning properties by simply varying the precursor and/or the synthesis parameters. Among the many appealing features of plasma-synthesized and -treated polymers, a highly reactive surface, rich in free radicals arising from deposition/treatment specifics, offers a particular advantage. When handled carefully, these reactive free radicals open doors to the controllable surface functionalization of materials without affecting their bulk properties. The goal of this review is to illustrate the increasing application of plasma-based technologies for tuning the surface properties of polymers, principally through free-radical chemistry.

Plasma polyacrylic acid and hollow TiO2 spheres modified with rhodamine B for sensitive electrochemical sensing Cu(ii)

A rhodamine B-modified nanocomposite-based electrochemical sensor was fabricated for selectively and sensitively detecting Cu(ii) in environmental fields.

Hydrophilic polymer/polypyrrole/graphene oxide nanosheets with different performances in electrocatalytic applications to simultaneously determine dopamine and ascorbic acid

Hydrophilic polymers functionalized polypyrrole/graphene oxide nanosheets were successfully synthesized and presented different performance for simultaneous determination to DA and AA.