A TiO 2 nanosheet-g-C 3 N 4 composite photoelectrochemical enzyme biosensor excitable by visible irradiation

Unlocking the potential of titanium dioxide nanoparticles: an insight into green synthesis, optimizations, characterizations, and multifunctional applications

This comprehensive review explores the emergence of titanium dioxide nanoparticles (TiO2-NPs) as versatile nanomaterials, particularly exploring their biogenic synthesis methods through different biological entities such as plants, bacteria, fungi, viruses, and algae. These biological entities provide eco-friendly, cost-effective, biocompatible, and rapid methods for TiO2-NP synthesis to overcome the disadvantages of traditional approaches. TiO2-NPs have distinctive properties, including high surface area, stability, UV protection, and photocatalytic activity, which enable diverse applications. Through detailed analysis, this review demonstrates significant applications of green fabricated TiO2-NPs in biomedicine, explicitly highlighting their antimicrobial, anticancer, and antioxidant activities, along with applications in targeted drug delivery, photodynamic therapy, and theragnostic cancer treatment. Additionally, the review underscores their pivotal significance in biosensors, bioimaging, and agricultural applications such as nanopesticides and nanofertilizers. Also, this review proves valuable incorporation of TiO2-NPs in the treatment of contaminated soil and water with various environmental contaminants such as dyes, heavy metals, radionuclides, agricultural effluents, and pathogens. These comprehensive findings establish the foundation for future innovations in nanotechnology, underscoring the importance of further investigating bio-based synthetic approaches and bioactivity mechanisms to enhance their efficacy and safety across healthcare, agricultural, and environmental applications.

Emerging Roles of Graphitic Carbon Nitride-based Materials in Biomedical Applications

Graphite carbon nitride (g-C3N4) is a two-dimensional conjugated polymer with a unique energy band structure similar to graphene. Due to its outstanding analytical advantages, such as relatively small band gap (2.7 eV), low-cost synthesis, high thermal stability, excellent photocatalytic ability, and good biocompatibility, g-C3N4 has attracted the interest of researchers and industry, especially in the medical field. This paper summarizes the latest research on g-C3N4-based composites in various biomedical applications, including therapy, diagnostic imaging, biosensors, antibacterial, and wearable devices. In addition, the application prospects and possible challenges of g-C3N4 in nanomedicine are also discussed in detail. This review is expected to inspire emerging biomedical applications based on g-C3N4.

ZIF-67 Anchored on MoS2/rGO Heterostructure for Non-Enzymatic and Visible-Light-Sensitive Photoelectrochemical Biosensing

Graphene and graphene-like two-dimensional layered nanomaterials-based photoelectrochemical (PEC) biosensors have recently grown rapidly in popularity thanks to their advantages of high sensitivity and low background signal, which have attracted tremendous attention in ultrahigh sensitive small molecule detection. This work proposes a non-enzymatic and visible-light-sensitive PEC biosensing platform based on ZIF-67@MoS2/rGO composite which is synthesized through a facile and one-step microwave-assisted hydrothermal method. The combination of MoS2 and rGO could construct van der Waals heterostructures, which not only act as visible-light-active nanomaterials, but facilitate charge carriers transfer between the photoelectrode and glassy carbon electrode (GCE). ZIF-67 anchored on MoS2/rGO heterostructures provides large specific surface areas and a high proportion of catalytic sites, which cooperate with MoS2 nanosheets, realizing rapid and efficient enzyme-free electrocatalytic oxidation of glucose. The ZIF-67@MoS2/rGO-modified GCE can realize the rapid and sensitive detection of glucose at low detection voltage, which exhibits a high sensitivity of 12.62 μAmM-1cm-2. Finally, the ZIF-67@MoS2/rGO PEC biosensor is developed by integrating the ZIF-67@MoS2/rGO with a screen-printed electrode (SPE), which exhibits a high sensitivity of 3.479 μAmM-1cm-2 and a low detection limit of 1.39 μM. The biosensor's selectivity, stability, and repeatability are systematically investigated, and its practicability is evaluated by detecting clinical serum samples.

Self-powered biosensor using photoactive ternary nanocomposite: Testing the phospholipid content in rhodotorula glutinis oil

In the field of oil refining, the presence of excessive residual phosphorus in crude oil can significantly impact its quality, thereby emphasizing the necessity for compact and convenient testing equipment. This study primarily focuses on developing of self-powered biosensor (SPB) using immobilizing Choline Oxidase with a photoactive ternary nanocomposite complex (CHOx-BiOI-rGO-Fe3O4 NPs-ITO) as the anode and utilizing a Pt electrode as the cathode. The successful preparation of the ternary composite photoelectrode for the anode was confirmed through a range of characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), N2 absorption/desorption, Dynamic light scattering (DLS), and Ultraviolet-visible diffuse reflection spectrometer (UV-vis DRS). The electrochemical and photoelectrochemical properties were assessed using an electrochemical workstation, revealing a significant enhancement photoelectrical responsiveness attributed to the formation of heterojunction structures. The SPB exhibited a remarkable linear relationship between the instantaneous photocurrent and phosphatidylcholine (PC) concentration, with a regression equation of I (μA) = 39.62071C (mM) + 3.47271. The linear range covered a concentration range of 0.01-10 mM, and the detection limit (S/N = 3) was determined to be 0.008 mM. It demonstrated excellent reproducibility and storage stability, positioning it a promising alternative to High-performance liquid chromatography (HPLC) for accurate quantification of PC content in rhodotorula glutinis oil. The standard recovery PC content ranged from 98.48% to 103.53%, with a relative standard deviation (RSD) ranging from 1.4% to 2.4%. This research presents a convenient and precise detection device that has the potential to address the issue of lagging detection in the oil refining process.

Development of Two-Dimensional Functional Nanomaterials for Biosensor Applications: Opportunities, Challenges, and Future Prospects

New possibilities for the development of biosensors that are ready to be implemented in the field have emerged thanks to the recent progress of functional nanomaterials and the careful engineering of nanostructures. Two-dimensional (2D) nanomaterials have exceptional physical, chemical, highly anisotropic, chemically active, and mechanical capabilities due to their ultra-thin structures. The diversity of the high surface area, layered topologies, and porosity found in 2D nanomaterials makes them amenable to being engineered with surface characteristics that make it possible for targeted identification. By integrating the distinctive features of several varieties of nanostructures and employing them as scaffolds for bimolecular assemblies, biosensing platforms with improved reliability, selectivity, and sensitivity for the identification of a plethora of analytes can be developed. In this review, we compile a number of approaches to using 2D nanomaterials for biomolecule detection. Subsequently, we summarize the advantages and disadvantages of using 2D nanomaterials in biosensing. Finally, both the opportunities and the challenges that exist within this potentially fruitful subject are discussed. This review will assist readers in understanding the synthesis of 2D nanomaterials, their alteration by enzymes and composite materials, and the implementation of 2D material-based biosensors for efficient bioanalysis and disease diagnosis.

Two-Dimensional Graphitic Carbon Nitride (g-C3N4) Nanosheets and Their Derivatives for Diagnosis and Detection Applications

The early diagnosis of certain fatal diseases is vital for preventing severe consequences and contributes to a more effective treatment. Despite numerous conventional methods to realize this goal, employing nanobiosensors is a novel approach that provides a fast and precise detection. Recently, nanomaterials have been widely applied as biosensors with distinctive features. Graphite phase carbon nitride (g-C3N4) is a two-dimensional (2D) carbon-based nanostructure that has received attention in biosensing. Biocompatibility, biodegradability, semiconductivity, high photoluminescence yield, low-cost synthesis, easy production process, antimicrobial activity, and high stability are prominent properties that have rendered g-C3N4 a promising candidate to be used in electrochemical, optical, and other kinds of biosensors. This review presents the g-C3N4 unique features, synthesis methods, and g-C3N4-based nanomaterials. In addition, recent relevant studies on using g-C3N4 in biosensors in regard to improving treatment pathways are reviewed.

2D Material-Based Optical Biosensor: Status and Prospect

The combination of 2D materials and optical biosensors has become a hot research topic in recent years. Graphene, transition metal dichalcogenides, black phosphorus, MXenes, and other 2D materials (metal oxides and degenerate semiconductors) have unique optical properties and play a unique role in the detection of different biomolecules. Through the modification of 2D materials, optical biosensor has the advantages that traditional sensors (such as electrical sensing) do not have, and the sensitivity and detection limit are greatly improved. Here, optical biosensors based on different 2D materials are reviewed. First, various detection methods of biomolecules, including surface plasmon resonance (SPR), fluorescence resonance energy transfer (FRET), and evanescent wave and properties, preparation and integration strategies of 2D material, are introduced in detail. Second, various biosensors based on 2D materials are summarized. Furthermore, the applications of these optical biosensors in biological imaging, food safety, pollution prevention/control, and biological medicine are discussed. Finally, the future development of optical biosensors is prospected. It is believed that with their in-depth research in the laboratory, optical biosensors will gradually become commercialized and improve people's quality of life in many aspects.

A highly sensitive photoelectrochemical aptasensor based on BiVO4 nanoparticles-TiO2 nanotubes for detection of PCB72

In this work, a simple and highly sensitive photoelectrochemical (PEC) aptasensor has been developed for detecting PCB72 based on TiO₂ nanotubes (NTs) decorated with BiVO₄ nanoparticles (NPs). The BiVO₄ NPs-TiO₂ NTs composites prepared through a simple hydrothermal method exhibit good visible-light adsorption ability, high PEC response and perfect photo-excited stability. The synthesized composites were explored as the photoactive sensing materials for development of a PEC sensing platform for the first time. Here, Au nanoparticles (NPs) were first deposited the composites, and the anti-PCB72 aptamer molecules were immobilized on the Au NPs-deposited BiVO₄ NPs-TiO₂ NTs. The developed PEC aptasensor exhibits high sensitivity and specificity for PCB72 with a wide linear range from 1 ng/L to 500 ng/L and a low detection limit of 0.23 ng/L. The application of the aptasensor was evaluated by determining PCB 72 in the environment water samples. Thus, a simple and efficient PEC sensing platform was established for detecting the content of PCBs in the environment.

Mesoporous TiO2-based architectures as promising sensing materials towards next-generation biosensing applications

In the past two decades, mesoporous TiO2 has emerged as a promising material for biosensing applications. In particular, mesoporous TiO2 materials with uniform, well-organized pores and high surface areas typically exhibit superior biosensing performance, which includes high sensitivity, broad linear response, low detection limit, good reproducibility, and high specificity. Therefore, the development of biosensors based on mesoporous TiO2 has significantly intensified in recent years. In this review, the expansion and advancement of mesoporous TiO2-based biosensors for glucose detection, hydrogen peroxide detection, alpha-fetoprotein detection, immobilization of enzymes, proteins, and bacteria, cholesterol detection, pancreatic cancer detection, detection of DNA damage, kanamycin detection, hypoxanthine detection, and dichlorvos detection are summarized. Finally, the future perspective and research outlook on the utilization of mesoporous TiO2-based biosensors for the practical diagnosis of diseases and detection of hazardous substances are also given.

Photoelectrochemical performance of facet-controlled TiO2 nanosheets grown hydrothermally on FTO

Single crystal anatase TiO₂ nanosheets (TiO₂-NSs) are grown hydrothermally on fluorine-doped tin oxide (FTO). By systematically changing the hydrothermal conditions such as reaction time, initial concentration of Ti precursor, F precursor, and HCl as an additive, a wide variety of TiO₂-NSs, with different morphologies and faceting have been synthesized. For the different morphologies and different facet ratios (anatase S ₀₀₁/S _001+101), the photoelectrochemical response is characterized and compared. We find that for photoanodes in neutral electrolytes, the magnitude of the photocurrent depends strongly on the growth parameters, that is, peak IPCEs can vary from 11.7% to 61%. For a wide range of parameters, the key parameter deciding on the photocurrent is the effective electrochemically active area of the electrode. Only for very high facet ratios >91%, the photoresponse can be strongly influenced by faceting - for samples with a S ₀₀₁/S _001+101 of 91%, IPCE value of ≈84% is obtained. This work defines not only optimized synthesis conditions for a most effective growth of these single crystalline electrode, but also represents fundamental data for further applications of such electrodes.

Non-Carbon 2D Materials-Based Field-Effect Transistor Biosensors: Recent Advances, Challenges, and Future Perspectives

In recent years, field-effect transistors (FETs) have been very promising for biosensor applications due to their high sensitivity, real-time applicability, scalability, and prospect of integrating measurement system on a chip. Non-carbon 2D materials, such as transition metal dichalcogenides (TMDCs), hexagonal boron nitride (h-BN), black phosphorus (BP), and metal oxides, are a group of new materials that have a huge potential in FET biosensor applications. In this work, we review the recent advances and remarkable studies of non-carbon 2D materials, in terms of their structures, preparations, properties and FET biosensor applications. We will also discuss the challenges facing non-carbon 2D materials-FET biosensors and their future perspectives.

Enhancement of Biosensors by Implementing Photoelectrochemical Processes

Research on biosensors is growing in relevance, taking benefit from groundbreaking knowledge that allows for new biosensing strategies. Electrochemical biosensors can benefit from research on semiconducting materials for energy applications. This research seeks the optimization of the semiconductor-electrode interfaces including light-harvesting materials, among other improvements. Once that knowledge is acquired, it can be implemented with biological recognition elements, which are able to transfer a chemical signal to the photoelectrochemical system, yielding photo-biosensors. This has been a matter of research as it allows both a superior suppression of background electrochemical signals and the switching ON and OFF upon illumination. Effective electrode-semiconductor interfaces and their coupling with biorecognition units are reviewed in this work.

Metal Oxides-Based Semiconductors for Biosensors Applications

The present mini review contains a concessive overview on the recent achievement regarding the implementation of a metal oxide semiconductor (MOS) in biosensors used in biological and environmental systems. The paper explores the pathway of enhancing the sensing characteristics of metal oxides by optimizing various parameters such as synthesis methods, morphology, composition, and structure. Four representative metal oxides (TiO₂, ZnO, SnO₂, and WO₃) are presented based on several aspects: synthesis method, morphology, functionalizing molecules, detection target, and limit of detection (LOD).

Biomedical Applications of TiO2 Nanostructures: Recent Advances

Titanium dioxide (TiO2) nanostructures are one of the most plentiful compounds that have emerged in various fields of technology such as medicine, energy and biosensing. Various TiO2 nanostructures (nanotubes [NTs] and nanowires) have been employed in photoelectrochemical (PEC) biosensing applications, greatly enhancing the detection of targets. TiO2 nanostructures, used as reinforced material or coatings for the bare surface of titanium implants, are excellent additive materials to compensate titanium implants deficiencies-like poor surface interaction with surrounding tissues-by providing nanoporous surfaces and hierarchical structures. These nanostructures can also be loaded by diversified drugs-like osteoporosis drugs, anticancer and antibiotics-and used as local drug delivery systems. Furthermore, TiO2 nanostructures and their derivatives are new emerging antimicrobial agents to overcome human pathogenic microorganisms. However, like all other nanomaterials, toxicity and biocompatibility of TiO2 nanostructures must be considered. This review highlights recent advances, along with the properties and numerous applications of TiO2-based nanostructure compounds in nano biosensing, medical implants, drug delivery and antibacterial fields. Moreover, in the present study, some recent advances accomplished on the pharmaceutical applications of TiO2 nanostructures, as well as its toxicity and biocompatibility, are presented.

Detection signal amplification strategies at nanomaterial-based photoelectrochemical biosensors

This review focusses on unique material modification and signal amplification strategies reported in developing photoelectrochemical biosensors with utmost sensitivity and selectivity.

Enhanced photoelectrochemical biosensing performance for Au nanoparticle–polyaniline–TiO2 heterojunction composites

A new photoelectrochemical (PEC) sensing platform comprising TiO₂ nanotube arrays (TiONTAs), polyaniline (PANI), and gold nanoparticles (AuNPs) was successfully fabricated. After loading the enzyme, this Au–PANI–TiONTA electrode showed excellent response to glucose at a linear range of 2–36 mM with a 0.02 mM detection limit. Good PEC performance was obtained due to the following advantages of the material: high visible-light harvesting ability for excellent light trapping capacity of PANI and AuNPs, good separation of the photo-induced charges related to the specific Au–PANI–TiONTA heterostructure, efficient electrode surface reaction kinetics derived from the large specific surface area of TiONTAs and improved electrode catalytic activity. This work proposed a new and general PEC enzymatic format and can be extended to prepare different PEC biosensors for biomolecules such as DNA, proteins and substrates of oxidases.

A novel photoelectrode for glucose PEC biosensing composed of TiONTAs, PANI, and AuNPs was successfully obtained. The GOx@Au–PANI–TiONTA electrode exhibited a wide response range (2–36 mM) with a low detection limit (0.02 mM) and good stability.

Highly sensitive photoelectrochemical detection of bleomycin based on Au/WS2 nanorod array as signal matrix and Ag/ZnMOF nanozyme as multifunctional amplifier

An ultrasensitive photoelectrochemical (PEC) biosensor was constructed based on gold nanoparticles (Au NPs)/tungsten sulfide nanorod array (WS₂ NA) photoelectrode as the PEC matrix and silver nanoparticles/flake-like zinc metal-organic framework (Ag/ZnMOF) nanozyme with the peroxidase mimetic enzyme property for sensitive detection of bleomycin (BLM). In particular, Au/WS₂ and Ag/ZnMOF were linked by thiolate DNA₁ and DNA₂ strand, respectively, and the Au/WS₂-Ag/ZnMOF probe was prepared via hybridization reaction between the two DNAs. The introduction of Ag/ZnMOF in the probe offers two functions: i) the steric hindrance effect can effectively impede electron transport and reduce the photocurrent; ii) Ag/ZnMOF nanozyme can also be used as mimic peroxidase to effectively catalyze 3,3-diaminobenzidine (DAB) to produce the relevant precipitation, which will further reduce photocurrent and eliminate false positive signals. When BLM exists, BLM with Fe²⁺ as irreversible cofactor can specifically recognize and cleave of the 5'-GC-3' active site of DNA₂, resulting in reduced precipitation deposited on the electrode and recovery of PEC signal. The highly sensitive PEC biosensor exhibits a the linear strategy from 0.5 nM to 500 nM with a detection limit down to 0.18 nM. Further, the unique strategy was conducted in biological samples for BLM detection with satisfactory consequence, offering available and efficient pathway for disease diagnosis.

A visible light photoelectrochemical sandwich aptasensor for adenosine triphosphate based on MgIn2S4-TiO2 nanoarray heterojunction

This work designed a MgIn₂S₄-TiONA heterojunction by growing MgIn₂S₄ nanoplates on TiO₂ nanowire array (TiONA) for preparation of visible light photoelectrochemical (PEC) sensing platform. The heterojunction exhibited strong absorption of visible light, large surface area and high loading of biomolecules, leading to high sensing sensitivity. Using adenosine triphosphate (ATP), a marker of cell vitality, as the target model, a PEC sandwich aptasensor was constructed by immobilizing capture DNA₁ on MgIn₂S₄ surface. In the presence of ATP and signal DNA₂ with terminal ferrocene as the electron donor, a sandwiched DNA₁-ATP-DNA₂ complex could be formed on the PEC aptasensor. The aptasensor showed excellent performance with a wide linear range from 50 fM to 100 nM and a detection limit of 20 fM. The sensing performance including specificity, reproducibility, stability and practical use were also evaluated, showing promising application of the MgIn₂S₄-TiONA heterojunction in PEC biosensing.

Fabrication of protonated g-C3N4 nanosheets as promising proton conductive materials

Protonated g-C3N4 nanosheets were prepared by refluxing a mixture containing g-C3N4 and 95% H2SO4 at 80 °C for 1 hour. The obtained g-C3N4 nanosheets showed a similar layer structure to that of g-C3N4 and high water adsorption capacities. They also depicted superior conductivities reaching up to 1.44 × 10-2 S cm-1 at 80 °C and 98% RH, with promising features for proton conductivity materials.

In situ growth of carbon dots on TiO2 nanotube arrays for PEC enzyme biosensors with visible light response

Carbon dots (CDs) were grown in situ on secondary anodized TiO₂ nanotube arrays (TiO₂ NTAs) via a hydrothermal method. The combination of CDs and TiO₂ NTAs enhanced the photoelectrochemical performance. Morphology, structure, and elemental composition of the CDs were characterized. No simple physical adsorption was found between the CDs and TiO₂, but chemical bonds were formed. UV-vis absorption and fluorescence spectroscopy showed that the CDs could enhance the absorption of TiO₂ in the visible and near-infrared regions. Owing to their up-conversion fluorescence properties, the CDs could convert low-energy photon absorption into high-energy photons, which may be used to excite TiO₂ to produce a stronger photoelectric response. Moreover, the CDs could effectively transport electrons and accept holes, thus contributing to the effective separation of electrons and holes during photoexcitation. Finally, the PEC biosensor was prepared by immobilizing glucose oxidase (GOx) on the surface of the composite. The PEC biosensor exhibited a broad range of 0.1–18 mM with a detection limit of 0.027 mM under visible irradiation because the composite material reflected strong light absorption for visible light, good conductivity, and good biocompatibility.

Carbon dots (CDs) were grown in situ on secondary anodized TiO₂ nanotube arrays (TiO₂ NTAs) via a hydrothermal method.

A carbon-rich nanofiber framework based on a conjugated arylacetylene polymer for photocathodic enzymatic bioanalysis

The metal-free photocathode fabricated by porous carbon-rich nanofiber framework of PTEB film realized “signal-off” photocathodic bioanalysis of glucose.

An ultrasensitive photoelectrochemical biosensor for glucose based on bio-derived nitrogen-doped carbon sheets wrapped titanium dioxide nanoparticles

In this work, an ultra-sensing photoelectrochemical (PEC) glucose biosensor has been constructed from the bio-derived nitrogen-doped carbon sheets (NDC) wrapped titanium dioxide nanoparticles (NDC-TiO₂ NPs) followed by the covalent immobilization of glucose oxidase (GODx) on them (designated as a GODx/NDC-TiO₂NPs/ITO biosensor). Initially, the TiO₂ NPs was synthesized by sol-gel method and then NDC-TiO₂ NPs was synthesized utilizing a green source of Prunus persica (peach fruit) through a simple hydrothermal process. The synthesized NDC-TiO₂ NPs composite was characterized by FESEM, HRTEM, Raman spectroscopy, XRD, ATR-FTIR spectroscopy and XPS to determine composition and phase purity. These fabricated GODx/NDC-TiO₂NPs/ITO biosensor exhibited a good charge separation, highly enhanced and stable photocurrent responses with switching PEC behavior under the light (λ > 400 nm). As a result, GODx/NDC-TiO₂NPs/ITO PEC glucose sensor exhibits a good photocurrent response to detection of glucose concentrations (0.05-10 μM) with an ultra-low detection limit of 13 nM under optimized PEC experimental conditions. Also, the PEC glucose sensor revealed a high selectivity, good stability, long time durability, and capability to analyze the glucose levels in real human serum. Also, the further development of this work may provide new insights into preparing other bio-derived carbon nanostructure-based photocatalysts for PEC applications.