Congregating Ag into γ-Bi2O3 coupled with CoFe2O4 for enhanced visible light photocatalytic degradation of ciprofloxacin, Cr(VI) reduction and genotoxicity studies

The work attempts to construct a highly effective γ-Bi2O3/CoFe2O4/Ag visible active photocatalyst for the enhanced degradation of ciprofloxacin (CIP) and Cr(VI) reduction. γ-Bi2O3/CoFe2O4/Ag photocatalyst was prepared by simple solid phase and co-precipitation methods. The nanosphere shaped CoFe2O4 photocatalyst are embedded on top of γ-Bi2O3 nanotriangle. The addition of Ag into γ-Bi2O3/CoFe2O4 heterojunction primitively facilitates the photocatalytic activity in higher rate. The quantitative analysis of photocatalyst possesses to have lower e-/h+ recombination rate compared to its counterparts. The prepared γ-Bi2O3/CoFe2O4/Ag photocatalyst showed 96.6% degradation of CIP in 220 min and 99.2% reduction of Cr(VI) in 120 min. Additionally, γ-Bi2O3/CoFe2O4/Ag showed outstanding recyclability and long-term stability with a degradation efficiency of 96.5% even after six cycles. The intermediate products formed were identified and the degradation pathway was elucidated by gas chromatography-mass spectrometry analysis. Total organic carbon measurement was carried over to assess the efficiency of complete degradation and the removal percentage was found to be 98%. The end product toxicity study towards bacteria was proven to have less toxicity level when compared to parent compound. Lastly, the genotoxicity of γ-Bi2O3/CoFe2O4/Ag photocatalyst was tested in Allium cepa and the results confirmed to have no cause of toxicity impacts. Overall, the work not only tends to provide a highly visible active γ-Bi2O3/CoFe2O4/Ag photocatalyst, but also attributes to have no further negative imprints in the environment.

Ultrasensitive Ratiometric Fluorescence Bioassay for Accurate Detection of Covid-19-Specific Nucleocapsid Protein in Clinical Serum Samples Using Modified Cleavable Mesoporous SiO2 Satellite-Enriched Carbon Dots

Due to the presence of various autofluorescent compounds in biological samples like serum and the photobleaching of organic fluorophores, fluorescence sensing has limited practical applicability. This study describes the development of an improved ratiometric fluorescence assay to determine the nucleocapsid protein (N protein), one of the most conserved biomarkers of Covid-19 in spiked and serum samples using highly stable buffer-based near IR-dual emission carbon dots (CDs) encapsulated into the cavities of cleavable silica nanocapsule (SNCs) nanocomposite. The cavities of cleavable silica nanocapsules (SNCs) and the formed core-shell CDs@ SNCs were used as a superior reservoir of fluorescent markers produced by cohydrolyzing tetraethyl orthosilicate and diiminosilane linker, which held hundreds of CDs in silica shell frameworks. The SiO2 nanocomposite was modified with an N protein antibody that specifically paired to the receptor binding region of the Cov-19 spike protein subunit. CDs were taken out of SNCs by NaBH4 reduction, and the released CDs exhibited dual emission at 475 and 675 nm when excited at 400 nm. Ratiometric detection is completed over a binding-induced, concentration-dependent immuno-affinity of the N protein that drives the fluorescence quenching phenomenon between the CDs as fluorophore and the AuNPs as quencher. As the N protein concentration increased, the intensity of the red emission (675 nm) dropped, whereas the intensity of the green emission (475 nm) already remained constant, which is due to sandwich immunoassays of CDs around AuNPs. Using the exceptional fluorescent characteristics of CDs and the high selectivity of nanocomposite functionalized with N-protein antibody, the developed assay efficiently eliminates the autofluorescence background interference of serum samples. The fluorescence ratio (I475/I675) provides a limit of detection of 2 pg mL-1 over a linear range of 0.01 to 5 ng mL-1 and exhibits an amplified sensitivity of 54 times compared to conventional immunoassay using CDs as fluorescent labels. With one-step signal amplification and requiring small sample quantities (only 20 μL), this sensing platform can be effectively used for the accurate detection of N protein, and no cross-reactivity is detected in the presence of different interfering agents.

Ultrathin MXene nanosheet-based TiO2/CdS heterostructure as a photoelectrochemical sensor for detection of CEA in human serum samples

To develop highly accurate and ultrasensitive strategies is of great importance for the clinical measurement, in particular, the detection of cancer biomarkers. Herein, we synthesized an ultrasensitive TiO₂/MXene/CdS QDs (TiO₂/MX/CdS) heterostructure as a photoelectrochemical immunosensor, which favors energy levels matching and fast electron transfer from CdS to TiO₂ in the help of ultrathin MXene nanosheet. Dramatic photocurrent quenching can be observed upon incubation of the TiO₂/MX/CdS electrode by Cu²⁺ solution from 96-well microplate, which caused by the formation of CuS and subsequent Cu_xS (x = 1, 2), reducing the absorption of light and boosting the electron-hole recombination upon irradiation. As a result, the as-prepared biosensor demonstrates a linearly increased photocurrent quenching percentage (Q%) value with CEA concentration ranging from 1 fg/mL to 10 ng/mL, as well as a low detection limit of 0.24 fg/mL. Benefit from its excellent stability, high selectivity and good reproducibility of as-prepared PEC immunosensor, we believe that this proposed strategy might provide new opportunities for clinical diagnosis of CEA and other tumor markers.

An ultrasensitive split-type electrochemical immunosensor based on controlled-release strategy for detection of CA19-9

In this study, a novel split-type electrochemical immunosensor based on controlled release strategy was proposed for sensitive analysis and detection of tumor marker carbohydrate antigen 199 (CA19-9). Specifically, glucose (Glu) was encapsulated in carrier mesoporous silica (MSN) with encapsulation technology, and surface functionalized Zinc sulfide (ZnS) caps were used as "gatekeepers". The complex is formed by encapsulating Glu within MSN with ZnS (ZnS@MSN-Glu) as a signal amplifier labeled on the signal antibody (Ab₂). And the Ab₂ can detect the presence of antibodies. To reduce the interference of biological analysis, the immune recognition process of ZnS@MSN-Glu-Ab₂ bioconjugate and antigen was carried out in 96-well microplate, which did not interfere with the electrochemical analysis process. Therefore, the low sensitivity detection caused by biofouling of nanomaterials and immunoreaction on the testing platform is eliminated. Subsequently, the opening and timed release of mesopores were controlled by external stimuli, the disulfide bond cleavage by dithiothreitol (DTT), and glucose was effectively released. Then nickel cobalt layered double hydroxide (NiCo-LDH) were directly hydrothermally grown on carbon cloth (CC) electrodeposited with copper selenide (CuSe) nanosheets to construct three-dimensional (3D) cactus-like NiCo-LDH/CuSe/CC sensing platform. It can realize the catalytic oxidation of released glucose, triggering glucose-mediated signal amplification. The synergistic effect of the 3D cactus structure and active nanomaterials promotes electron conduction. Taking the detection of carbohydrate antigen CA19-9 as an example, the immunosensor shows a wide linear concentration range (0.001-100 U/mL) with the limit of detection of 0.0005 U/mL, realizing highly sensitive detection of CA19-9. This biosensing technique has considerable advantages and provides an innovative approach for trace detection of other biomarkers.

Detection of carcinoembryonic antigens using a wavy gold-silver alloy nanoplate enhanced surface plasmon resonance imaging biosensor

Carcinoembryonic antigen (CEA) is regarded as a promising broad spectrum tumor biomarker for clinical diagnosis, progression, and prognosis. Surface plasmon resonance imaging (SPRi) was considered as one of the powerful tools for immunoassay with advantages of label-free, real-time detection with high-throughput. Herein, wavy gold-silver alloy nanoplates functionalized with anti-CEA antibodies providing high protein loading capacity and high mass are used as signal enhancers for CEA detection through SPRi sandwich assay. The present method exhibits a dynamic range for CEA determination from 0.1 to 312.5 ng mL^-1 and a detection limit of 0.55 ng mL^-1, well below normal physiological levels. This biosensing approach demonstrates the advantages of wavy gold-silver alloy nanoplates compared to conventional gold nanoparticles as a signal amplifier to enhance the SPRi signal, which is expected to become a new prospect for detection of cancer markers in biomedical research and clinical diagnosis.

In Situ Formation of Bi2MoO6-Bi2S3 Heterostructure: A Proof-Of-Concept Study for Photoelectrochemical Bioassay of l-Cysteine

A novel signal-increased photoelectrochemical (PEC) biosensor for l-cysteine (L-Cys) was proposed based on the Bi₂MoO₆–Bi₂S₃ heterostructure formed in situ on the indium–tin oxide (ITO) electrode. To fabricate the PEC biosensor, Bi₂MoO₆ nanoparticles were prepared by a hydrothermal method and coated on a bare ITO electrode. When L-Cys existed, Bi₂S₃ was formed in situ on the interface of the Bi₂MoO₆/ITO electrode by a chemical displacement reaction. Under the visible light irradiation, the Bi₂MoO₆–Bi₂S₃/ITO electrode exhibited evident enhancement in photocurrent response compared with the Bi₂MoO₆/ITO electrode, owing to the signal-increased sensing system and the excellent property of the formed Bi₂MoO₆–Bi₂S₃ heterostructure such as the widened light absorption range and efficient separation of photo-induced electron–hole pairs. Under the optimal conditions, the sensor for L-Cys detection has a linear range from 5.0 × 10⁻¹¹ to 1.0 × 10⁻⁴ mol L⁻¹ and a detection limit of 5.0 × 10⁻¹² mol L⁻¹. The recoveries ranging from 90.0% to 110.0% for determining L-Cys in human serum samples validated the applicability of the biosensor. This strategy not only provides a method for L-Cys detection but also broadens the application of the PEC bioanalysis based on in situ formation of photoactive materials.

Mesoporous Silica Nanoparticles in Chemical Detection: From Small Species to Large Bio-Molecules

A recompilation of applications of mesoporous silica nanoparticles in sensing from the last five years is presented. Its high potential, especially as hybrid materials combined with organic or bio-molecules, is shown. Adding to the multiplying effect of loading high amounts of the transducer into the pores, the selectivity attained by the interaction of the analyte with the layer decorating the material is described. Examples of the different methodologies are presented.

Electrochemistry/Photoelectrochemistry-Based Immunosensing and Aptasensing of Carcinoembryonic Antigen

Recently, electrochemistry- and photoelectrochemistry-based biosensors have been regarded as powerful tools for trace monitoring of carcinoembryonic antigen (CEA) due to the fact of their intrinsic advantages (e.g., high sensitivity, excellent selectivity, small background, and low cost), which play an important role in early cancer screening and diagnosis and benefit people's increasing demands for medical and health services. Thus, this mini-review will introduce the current trends in electrochemical and photoelectrochemical biosensors for CEA assay and classify them into two main categories according to the interactions between target and biorecognition elements: immunosensors and aptasensors. Some recent illustrative examples are summarized for interested readers, accompanied by simple descriptions of the related signaling strategies, advanced materials, and detection modes. Finally, the development prospects and challenges of future electrochemical and photoelectrochemical biosensors are considered.

The toxicity analysis of PVP, PVA and PEG surface functionalized ZnO nanoparticles on embryonic as well as adult Danio rerio

Globally, the production of zinc oxide nanoparticles (ZnO NPs) increased due to its wide applications including cosmetics, paints etc., and gets accumulated in the environment during their production, use or end-of-life. The toxic effects of the NPs vary with the presence of various surface modification agents. In the current report, toxic effect of bare and capped ZnO NPs with polymeric surface modifying agent including polyvinyl alcohol (PVA), polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) is studied against adult as well as embryonic zebra fish. The surface capped NPs showed great variation in toxicity levels. It was observed that ZnO-PVA showed highly reduced toxic effects relative to ZnO-PEG and ZnO-PVP. Further, various environmental agents including humic acid can also have an impact on NPs toxicity. ZnO particles showed increased toxic effect in humic acid presence. The uptake of ZnO particles by D. rerio was high in the order of PVP-, PEG- and PVA- followed by bare-ZnO. The current investigation found that ZnO NPs dissolution and uptake are the major factors which cause the toxicity against adult as well as embryonic zebra fishes respectively.

A sandwich-type photoelectrochemical aptasensor using Au/BiVO4 and CdS quantum dots for carcinoembryonic antigen assay

A novel sandwich-type photoelectrochemical (PEC) aptasensor for the carcinoembryonic antigen (CEA) assay was fabricated using the CEA aptamer, Au/BiVO₄ and CdS quantum dots (CdS QDs). In virtue of the localized surface plasmon resonance effect of Au nanoparticles, Au/BiVO₄ showed an effective utilization of visible light and excellent photoactivity, and was employed as the photoanode. After CdS QDs were conjugated to Au/BiVO₄ through the sandwich structure based on the hybridization of the CEA aptamer with two partially complementary single-stranded DNA molecules, the photocurrents were further enhanced by a resonance energy transfer between CdS QDs and Au nanoparticles. Meanwhile, the consumption of the photo-induced holes by ascorbic acid could also retard the combination of the electron-hole pairs and cause an increase of the photocurrents. However, the specific recognition of CEA by the CEA aptamer could destroy the sandwich structure and remarkably weaken the photocurrent response. Thus, the quantitative detection of CEA was connected with the decrease of the photocurrent. Benefitting from the above methods for signal enhancement, the PEC aptasensor showed a wide sensing range of 0.0001-10 ng mL^-1 and a low detection limit of 0.047 pg mL^-1 for CEA detection. The specificity, stability and recoveries of the PEC aptasensor were also excellent. Therefore, the construction of the present PEC aptasensor provides a universal and practical method for sensing other substances.

Simulation and machine learning modelling based comparative study of InAlGaN and AlGaN high electron mobility transistors for the detection of HER-2

The detection of the cancer biomarker human epidermal growth factor receptor 2 (HER-2) has always been challenging at the early stages of cancer due to its very small presence. A systematic study of biosensors to achieve optimum sensitivity is of paramount significance. Thus, in this paper, we report a simulation study and machine learning (ML) based model for the comparative analysis of indium aluminum gallium nitride (InAlGaN) and aluminum gallium nitride (AlGaN) based high electron mobility transistors (HEMTs) for the detection of HER-2. The sensing performance of the InAlGaN based HEMT exhibits 1.8 times higher sensitivity as compared to that of the AlGaN based HEMT. The presented work also provides insights into the importance of the pH of the medium of HER-2. The results produced by the developed ML-based model are in good agreement with the simulation results. The model is not only capable of predicting within the trained range but also it can predict reasonably well even beyond the range of the training data. The introduction of a ML-based model significantly reduces the computational cost, time to perform similar type of simulations and, unlike the physics-based modelling, it also eliminates the need for empirical fitting of the model parameters.

Silica nanoparticle-modified microcomb electrode for voltammetry detection of osteopontin with high sensitivity

Osteosarcoma is a commonly occurring bone malignancy, and it is the second most common cause of cancer deaths in adolescents and children. A sensitive silica nanoparticle (Si-NP) modified current-volt sensor was introduced to identify the osteopontin antigen, a well-known biomarker for osteosarcoma. Si-NP was extracted from the rice husk ash and utilized for the surface functionalization on the interdigitated microelectrode sensing surface. Extracted Si-NP has a spherical shape with uniform distribution, and it is confirmed by field emission scanning electron microscopy and field-emission transmission electron microscopy. Si-NP was layered on the electrode surface through a (3-aminopropyl)triethoxysilane amine linker, and the antibody was immobilized on Si-NP through a glutaraldehyde linker. Osteopontin was effectively detected on the antibody-attached surface, and the determination limit was 0.6 ng/mL. The regression was determined as y = 0.9366x - 1.1113 and the R2 value was 0.9331 and the detection limit of osteopontin was 0.6 ng/mL in the range between 0.3 and 5 ng/mL. In addition, control performance with nonimmune antibodies and albumin did not change the current volt, showing the specific osteopontin identification. This research work brings out the easy and cost-effective method to diagnose osteosarcoma and its etiology.

Photogenerated Hole-Induced Chemical-Chemical Redox Cycling Strategy on a Direct Z-Scheme Bi2S3/Bi2MoO6 Heterostructure Photoelectrode: Toward an Ultrasensitive Photoelectrochemical Immunoassay

To achieve high sensitivity for biomolecule detection in photoelectrochemical (PEC) bioanalysis, the ideal photoelectrode and ingenious signaling mechanism play crucial roles. Herein, the feasibility of the photogenerated hole-induced chemical-chemical redox cycling amplification strategy on a Z-scheme heterostructure photoelectrode was validated, and the strategy toward enhanced multiple signal amplification for advanced PEC immunoassay application was developed. Specifically, a direct Z-scheme Bi₂S₃/Bi₂MoO₆ heterostructure was synthesized via a classic hydrothermal method and served as a photoelectrode for the signal response. Under the illumination, the PEC chemical-chemical redox cycling (PECCC) among 4-aminophenol generated by the enzymatic catalysis from a sandwich immunoassay, ferrocene as a mediator, and tris (2-carboxyethyl) phosphine as a reducing agent was run on the Z-scheme Bi₂S₃/Bi₂MoO₆ heterostructure photoelectrode. Exemplified by interleukin-6 (IL-6) as the target, the applicability of the strategy was studied in a PEC immunoassay. Thanks to the multiple signal amplification originating from the high efficiency of the PECCC redox cycling system, the enzymatic amplification, and the fine performance of the Z-scheme Bi₂S₃/Bi₂MoO₆ heterostructure photoelectrode, the assay for IL-6 exhibits a very low detection limit of 2.0 × 10^-14 g/mL with a linear range from 5.0 × 10^-14 to 1.0 × 10^-8 g/mL. This work first validates the feasibility of the PECCC redox cycling on the Z-scheme heterostructure photoelectrode and the good performance of the strategy in PEC bioanalysis. We envision that it would provide a new prospective for highly sensitive PEC bioanalysis on the basis of a Z-scheme heterostructure.

A versatile switchable dual-modal colorimetric and photoelectrochemical biosensing strategy via light-controlled sway of a signal-output transverter

A design criterion to construct a versatile dual-modal colorimetric and PEC biosensing platform for switching the corresponding mode freely is proposed via integration of a natural enzyme, light-activated nanozyme and light-controlled swayable signal-output transverter. A switchable dual-modal platform toward DNA analysis is developed as a proof of concept.

Biomedical application of mesoporous silica nanoparticles as delivery systems: a biological safety perspective

The application of mesoporous silica nanoparticles (MSNs) as drug delivery systems to deliver drugs, proteins, and genes has expanded considerably in recent years, using in vitro and animal studies. For future translation to clinical applications, the biological safety aspects of MSNs must be considered carefully. This paper reviews the biosafety of MSNs, examining key issues such as biocompatibility, effects on immune cells and erythrocytes, biodistribution, biodegradation and clearance, and how these vary depending on the effects of the physical and chemical properties of MSNs such as particle size, porosity, morphology, surface charge, and chemical modifications. The future use of MSNs as a delivery system must extend beyond what has been learnt thus far using rodent animal models to encompass larger animals.

Liposome encapsulated electron donor strategy for signal-on CYFRA 21-1 photoelectrochemical analysis

A novel electron donor controlled-release system is proposed based on liposome encapsulated L-cysteine for the sensitive determination of cytokeratin 19 fragment 21-1 (CYFRA 21-1). On the one hand, a defective TiO₂ modified with methylene blue was employed as a photoactive platform which exhibited a high photoelectrochemical (PEC) response owing to the introduction of oxygen vacancies and the high  photosensitivity of the dye. On the other hand, L-cysteine as the sacrificial electron donor was encapsulated in the vesicles of liposomes, and this composite was used as the signal amplification factor, which is labeled on the secondary antibody of CYFRA 21-1 to further improve the photocurrent sensitivity. The excellent electron transfer path in photoactive materials coupled with the skilful electron donor controlled-release system, contributed to the sensitive  PEC analysis of CYFRA 21-1 underoptimum conditions. The PEC immunoassay showed a linear current response in the range 0.0001-100 ng/mL with a detection limitof 37 fg/mL. Enhanced stability and satisfactory reproducibility were also achieved. The proposed concept  provides a novel signal-on strategy for the sensitive detection of other cancer markers in the electrochemical sensing field.

In situ creation of ZnO@CdS nanoflowers on ITO electrodes for sensitive photoelectrochemical detection of copper ions in blood

A highly selective and sensitive photoelectrochemical (PEC) detection method has been developed for the analysis of copper (Cu2+) ions using nanoflower-like ZnO@CdS heterojunctions, of which ZnO was first in situ grown onto the indium tin oxide electrodes by a hydrothermal method and then coated with CdS through the chemical bath deposition route. It was discovered that the ZnO@CdS heterojunction so formed could serve as a photosensitive catalyst with improved charge separation for visible-light-driven PEC responses. Enhanced visible-light harvesting of nanocomposites could also be expected with CdS as the visible-light sensitizer. Furthermore, the introduction of Cu2+ ions could cause a rational decrease in the photocurrents of nanocomposites through the specific interaction between CdS and Cu2+ ions. A ZnO@CdS heterojunction-based PEC sensor was thereby developed for the detection of Cu2+ ions in blood in the linear concentrations ranging from 0.50 to 80 nM, with a limit of detection of 0.18 nM. Such a heterojunction-based PEC detection platform constructed using two photocatalytic materials with matched band structures are promising for a wide range of applications for sensing Cu2+ ions in clinical diagnostics, food monitoring, and environmental analysis.

Aptamer based recognition of cancer cells: Recent progress and challenges in bioanalysis

Rapid and accurate monitoring of cancer cells with high sensitivity is essential for a successful cancer treatment. As high-affinity nucleic acid ligands, aptamers can improve the properties of detection methods by conjugating with intracellular or extracellular cancer biomarkers. Despite the advances in the early detection and treatment of cancer cells, lacking effective early detection tools is one of the causes of a high mortality rate. Aptasensors, which are based on the specificity of aptamer-target recognition, with transduction for analytical purposes have received particular attention due to their high sensitivity and selectivity, simple instrumentation, as well as low production cost. In this review, some selective and sensitive methods were summarized based on advanced nanomaterials towards aptasensing of cancer cells, such as blood, breast, cervical, colon, gastric, liver, and lung cancer cells. This review summarizes advances from 2010 to June 2020 in the development of aptasensors for cancer cell detection. Various aptasensing strategies are assessed according to their potential for reaching relevant limits of sensitivity, specificity, and degrees of multiplexing. Furthermore, we address the remaining challenges and opportunities to integrate aptasensing platforms into point-of-care solutions. Finally, the advantages and limitations of aptamer-based aptasensing strategies were reviewed.

Novel Electron Donor Encapsulation Assay Based on the Split-type Photoelectrochemical Interface

In this research, a controlled-release photoelectrochemical (PEC) immunosensor is proposed on the basis of a novel encapsulation strategy by all-inorganic semiconductor materials. The controlled-release transmit system has been prepared and represented on account of a group-functional mesoporous silica nanosphere (MSN), utilizing surface-functionalized cadmium sulfide (CdS) nanoparticles as mobilizable caps to encapsulate a PEC electron donor ascorbic acid (AA) within the MSN mesoporous structure. This encapsulation strategy proceeds without any enzyme and acid/alkali to achieve the release of an electron donor. The complex is formed by encapsulating AA within MSN with CdS (CdS@MSN-AA) as a signal amplifier labeled on the secondary antibody. In addition, the immunological recognition process was performed in a 96-well plate, and the reciprocal interference between biorecognition and PEC analysis could be eliminated through a split-type framework. Bi₂S₃-sensitized porous In₂O₃ nanoparticles as a substrate matrix provide basic PEC response. The developed sensor exhibited a mensurable output of procalcitonin (PCT) concentration (as an example) in the detection range of 0.001-200 ng/mL along with a limit of detection of 0.31 pg/mL. Featuring the novel method for electron release, this sensitive PEC strategy provides an innovative way for the potential application for other targets.

Ultrasensitive photoelectrochemical sensor enabled by a target-induced signal quencher release strategy

In this work, a target-induced signal quencher release strategy was proposed to construct a sensitive photoelectrochemical (PEC) sensor.

A single-interface photoelectrochemical sensor based on branched TiO2 nanorods@strontium titanate for the detection of two biomarkers

Based on the enhanced photogenerated charge-separation properties of B-TiO₂ NRs@SrTiO₃ heterostructures, a photoelectrochemical sensor for detecting alpha fetoprotein and cancer antigen 153 at a single interface was first established.