Periodical 2D Photonic-Plasmonic Au/TiOx Nanocavity Resonators for Photoelectrochemical Applications

Photonic-plasmonic resonator for SERS biodetection

To improve the laser utilization efficiency and avoid photodamage in surface-enhanced Raman spectroscopy (SERS), it is imperative to introduce photon technology into the field of SERS detection. A major challenge is the inefficient interaction between the substrate and the incident wavelength, resulting in limited Raman enhancement at a relatively low level. Here, we sputtered plasmonic Au nanoparticles (NPs) onto photonic TiOx nanocavities, creating a novel hybrid photonic-plasmonic resonator that achieves a large degree of optical manipulation and long-term localization. By facilely controlling the size of Au NPs, the resonance wavelength of plasmonic Au NPs can be matched with the photonic nanocavity to maximize the light trapping intensity, which leads to a synergistic enhancement of SERS via the electromagnetic and chemical mechanisms, resulting in a SERS enhancement up to 1.75 × 109 under non-resonant excitation. In particular, the substrate can achieve strong absorption and localization for long wavelengths, thus enabling a large SERS enhancement with a small light intensity, which can effectively avoid the photodamage that may occur in Raman testing. The substrate can detect various biomolecules, including biomarkers in serum, thus realizing the differentiation of different cancers. This study provides a powerful and sensitive platform for SERS, facilitating bioanalysis and disease diagnosis in complex systems.

Optical and Electrical Modulation Strategies of Photoelectrodes for Photoelectrochemical Water Splitting

When constructing efficient, cost-effective, and stable photoelectrodes for photoelectrochemical (PEC) systems, the solar-driven photo-to-chemical conversion efficiency of semiconductors is limited by several factors, including the surface catalytic activity, light absorption range, carrier separation, and transfer efficiency. Accordingly, various modulation strategies, such as modifying the light propagation behavior and regulating the absorption range of incident light based on optics and constructing and regulating the built-in electric field of semiconductors based on carrier behaviors in semiconductors, are implemented to improve the PEC performance. Herein, the mechanism and research advancements of optical and electrical modulation strategies for photoelectrodes are reviewed. First, parameters and methods for characterizing the performance and mechanism of photoelectrodes are introduced to reveal the principle and significance of modulation strategies. Then, plasmon and photonic crystal structures and mechanisms are summarized from the perspective of controlling the propagation behavior of incident light. Subsequently, the design of an electrical polarization material, polar surface, and heterojunction structure is elaborated to construct an internal electric field, which serves as the driving force to facilitate the separation and transfer of photogenerated electron-hole pairs. Finally, the challenges and opportunities for developing optical and electrical modulation strategies for photoelectrodes are discussed.

Zwitterionic Polymers Coating Antibiofouling Photoelectrochemical Aptasensor for In Vivo Antibiotic Metabolism Monitoring and Tracking

Long-term in vivo monitoring and tracking of target molecules in living organism is essential to reveal vital physiological activity. However, undesirable contamination of protein and biological cells may bring serious biofouling issues. Herein, zwitterionic sulfobetaine methacrylate (SBMA) polymers are grafted on the TiO₂ nanotube (NT) surface with polydopamine (PDA) as linker to fabricate a TiO₂ NTs/PDA/SBMA photoelectrode. The TiO₂ NTs/PDA/SBMA/aptamer-based PEC aptasensor can be sensitive and have selective detection of target molecules with excellent antibiofouling activity. Beneficial from the above advantages, the implantable micro-PEC aptasensor has implemented in vivo tracking and monitoring of the metabolism of antibiotics in a living mouse. The robust antibiofouling property generates new inquiries and an approach for long-standing questions in a new way for reliable and long-term sensing of vital biomolecules in complex biological fluids and uncovers a promising advance of intrinsic physiological mechanisms.

Recent Advances of Nanostructured Materials for Photoelectrochemical Bioanalysis

Nowadays, the emerging photoelectrochemical (PEC) bioanalysis has drawn intensive interest due to its numerous merits. As one of its core elements, functional nanostructured materials play a crucial role during the construction of PEC biosensors, which can not only be employed as transducers but also act as signal probes. Although both chemical composition and morphology control of nanostructured materials contribute to the excellent analytical performance of PEC bioassay, surveys addressing nanostructures with different dimensionality have rarely been reported. In this review, according to classification based on dimensionality, zero-dimensional, one-dimensional, two-dimensional, and three-dimensional nanostructures used in PEC bioanalysis are evaluated, with an emphasis on the effect of morphology on the detection performances. Furthermore, using the illustration of recent works, related novel PEC biosensing patterns with promising applications are also discussed. Finally, the current challenges and some future perspectives in this field are addressed based on our opinions.

Gold Nanoparticles Photosensitization towards 3,4,9,10-Perylenetetracarboxylic Dianhydride Integrated with a Dual-Particle Three-Dimensional DNA Roller: A General "ON-OFF-ON" Photoelectric Plasmon-Enhanced Biosensor

A high initial signal for the sensitive detection of analytes is critical in photoelectrochemical (PEC) biosensing systems. As a semiconductor, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) possesses an appropriate optical band gap of 2.5 eV and inherently intense and stable PEC response. When gold nanoparticles (Au NPs) are electrodeposited on the surface of PTCDA to form a Schottky junction (Au NPs/PTCDA), a surprising and satisfactory PEC performance is unfolded before our eyes. Considering the outstanding PEC behaviors of Au NPs/PTCDA and the great quenching effect of gold nanoclusters (Au NCs), the "ON-OFF-ON" PEC sensing platform has been developed for microRNA 1246 (miRNA 1246) detection combined with the cascaded quadratic amplification strategy of the polymerization/nicking reaction and dual-particle 3D DNA roller. The higher initial PEC signals of the system can be acquired by regulating the deposition time for 35 s (-0.2 V), which is derived from the synergetic effect of localized surface plasmon resonance of Au NPs and the formation of a Schottky junction. The dual-particle 3D DNA roller has been designed to guarantee wide walking space, remarkable operation performances, and inhibition of derailment. The proposed biosensor shows a dynamic range from 10 aM to 1 pM at a low detection limit of 3.1 aM and exhibits good analytical behaviors while analyzing miRNA 1246 in healthy human serum samples. This work not only expands the application of organic photoelectric materials in bioanalysis but also provides potential possibility of detecting other biomarkers by choosing appropriate target units.

A highly sensitive and group-targeting aptasensor for total phthalate determination in the environment

As the most widely used and typical kind of plasticizers, phthalate esters (PAEs) have become one of the most common environmental pollutants in the world. Therefore, it is necessary to develop a rapid and convenient method for determining the total amount of PAEs. Herein, a molecularly tailored broad-spectrum aptamer that can recognize multiple similarly structured total amounts of PAEs (TP) and bind them with high affinity has been successfully fabricated. Mfold (multiple folding) secondary structure simulation and molecular truncation were both utilized to obtain the most effective binding region from the parental full-length (39-mer) aptamer. The results show that the PAE-binding affinity of the truncated 24-mer aptamer produced by removing nonessential flanking nucleotides was improved by 1.5-fold. The linear range of TP detection is 0.003-10 μg/L, and the limit of detection is 1 ng/L. Notably, our study provides new insights into the group-targeting identification of certain pollutants and determination of their total amounts, exhibiting great potential for practical applications.

In Situ Synthesis of α-Fe2O3/Fe3O4 Heterojunction Photoanode via Fast Flame Annealing for Enhanced Charge Separation and Water Oxidation

Hematite (α-Fe₂O₃) is a promising photoanode material in photoelectrochemical (PEC) water splitting. To further improve the catalytic activity, a reasonable construction of heterojunction and surface engineering can effectively improve the photoanode PEC water-splitting performance via improving bulk carrier transport and interfacial charge-transfer efficiency. As Fe₃O₄ has an excellent conductivity and a suitable energy band position, α-Fe₂O₃/Fe₃O₄ heterojunction can be an ideal structure to improve the activity of α-Fe₂O₃. However, only few studies have been reported on α-Fe₂O₃/Fe₃O₄ heterojunctions as photoanodes. In this work, a holey nanorod Fe₂O₃/Fe₃O₄ heterojunction photoanode with oxygen vacancies was fabricated using a rapid and facile flame reduction treatment. Compared with pure Fe₂O₃, the water oxidation performance of the Fe₂O₃/Fe₃O₄ photoanode is improved by ninefold at 1.23 V_RHE. Our study revealed that the porous nanorod structure providing more active sites and oxygen vacancies as the hole transfer medium, together improve the interface charge transfer performance of the photoanode. At the same time, Fe₃O₄ can form a Fe₂O₃/Fe₃O₄ heterojunction to improve the carrier separation efficiency. More importantly, Fe₃O₄ can serve as active sites, solving the slow water oxidation kinetic problem of hematite to enhance the catalytic activity. Our work shows that when flame acts on precursors containing oxygen or hydroxide, it is easy to form compounds with different microstructures or compositions in situ.

Recent Advances in Plasmonic Perovskite Solar Cells

Perovskite solar cells (PSCs) have emerged recently as promising candidates for next generation photovoltaics and have reached power conversion efficiencies of 25.2%. Among the various methods to advance solar cell technologies, the implementation of nanoparticles with plasmonic effects is an alternative way for photon and charge carrier management. Surface plasmons at the interfaces or surfaces of sophisticated metal nanostructures are able to interact with electromagnetic radiation. The properties of surface plasmons can be tuned specifically by controlling the shape, size, and dielectric environment of the metal nanostructures. Thus, incorporating metallic nanostructures in solar cells is reported as a possible strategy to explore the enhancement of energy conversion efficiency mainly in semi-transparent solar cells. One particularly interesting option is PSCs with plasmonic structures enable thinner photovoltaic absorber layers without compromising their thickness while maintaining a high light harvest. In this Review, the effects of plasmonic nanostructures in electron transport material, perovskite absorbers, the hole transport material, as well as enhancement of effective refractive index of the medium and the resulting solar cell performance are presented. Aside from providing general considerations and a review of plasmonic nanostructures, the current efforts to introduce these plasmonic structures into semi-transparent solar cells are outlined.

Rationally Engineered Photonic-Plasmonic Synergistic Resonators in Second Near-Infrared Window for in Vivo Photoelectrochemical Biodetection

The introduction of photonic technologies into biodetection fields is in high demand to accelerate understanding vital movements at the molecular level. Great difficulty lies in the fact that the short penetration of photons in biotissues limits the practical applications of in vivo biodetection. Herein, we overcome this long-standing technical challenge through first introducing a new synergistic photonic-plasmonic resonator in second near-infrared window to realize efficient light trapping in this "bio-transparent zone". The well-match of photonic and plasmonic resonances in the same wavelength significantly increases the light-matter interplay activity, with 60% increase of quality factors, thus allowing us to pioneeringly implement the sensitive photoelectrochemical in vivo biodetection of macrophage cells in the tail vein of a living mouse. These synergistic photonic-plasmonic resonators promise bridges between vital photonic phenomena and practical biodetections or clinical applications.

Unprecedented efficient electron transport across Au nanoparticles with up to 25-nm insulating SiO2-shells

Quantum tunneling is the basis of molecular electronics, but often its electron transport range is too short to overcome technical defects caused by downscaling of electronic devices, which limits the development of molecular-/nano-electronics. Marrying electronics with plasmonics may well present a revolutionary way to meet this challenge as it can manipulate electron flow with plasmonics at the nanoscale. Here we report on unusually efficient temperature-independent electron transport, with some photoconductivity, across a new type of junction with active plasmonics. The junction is made by assembly of SiO₂ shell-insulated Au nanoparticles (Au@SiO₂ NPs) into dense nanomembranes of a few Au@SiO₂ layers thick and transport is measured across these membranes. We propose that the mechanism is plasmon-enabled transport, possibly tunneling (as it is temperature-independent). Unprecedentedly ultra-long-range transport across one, up to even three layers of Au@SiO₂ in the junction, with a cumulative insulating (silica) gap up to 29 nm/NP layer was achieved, well beyond the measurable limit for normal quantum mechanical tunneling across insulators (~2.5 nm at 0.5–1 V). This finding opens up a new interdisciplinary field of exploration in nanoelectronics with wide potential impact on such areas as electronic information transfer.

A composite prepared from BiOBr and gold nanoparticles with electron sink and hot-electron donor properties for photoelectrochemical aptasensing of tetracycline

A photoelectrochemical (PEC) aptasensor is described for detecting tetracycline (TC). A gold nanoparticles/BiOBr (AuNPs/BiOBr) composite was prepared where the AuNPs play a key function in carrier transfer which is ascribed to the wavelength-dependent dual function as an electron sink and as a hot-electron donor. Due to this dual function, the composite exhibits a wide photo-response and high electron transfer efficiency. This results in enormously enhanced PEC response. The TC-aptamer was immobilized on an ITO modified with AuNPs/BiOBr via Au-S covalent bonding. The resulting PEC aptasensor possesses a wide linear range (1-10⁴ ng L^-1) and a low detection limit (0.35 ng L^-1; at S/N = 3). Graphical abstractSchematic representation of a photoelectrochemical aptasensor for tetracycline based on the use of a AuNP/BiOBr composite with electron sink and hot-electron donor properties of the gold nanoparticles.

Affinity-Based Detection of Biomolecules Using Photo-Electrochemical Readout

Detection and quantification of biologically-relevant analytes using handheld platforms are important for point-of-care diagnostics, real-time health monitoring, and treatment monitoring. Among the various signal transduction methods used in portable biosensors, photoelectrochemcial (PEC) readout has emerged as a promising approach due to its low limit-of-detection and high sensitivity. For this readout method to be applicable to analyzing native samples, performance requirements beyond sensitivity such as specificity, stability, and ease of operation are critical. These performance requirements are governed by the properties of the photoactive materials and signal transduction mechanisms that are used in PEC biosensing. In this review, we categorize PEC biosensors into five areas based on their signal transduction strategy: (a) introduction of photoactive species, (b) generation of electron/hole donors, (c) use of steric hinderance, (d) in situ induction of light, and (e) resonance energy transfer. We discuss the combination of strengths and weaknesses that these signal transduction systems and their material building blocks offer by reviewing the recent progress in this area. Developing the appropriate PEC biosensor starts with defining the application case followed by choosing the materials and signal transduction strategies that meet the application-based specifications.

Near-Infrared-Responsive Photoelectrochemical Aptasensing Platform Based on Plasmonic Nanoparticle-Decorated Two-Dimensional Photonic Crystals

The photoelectrochemical (PEC) analysis is an emerging and fast developing biosensing technique. However, the in vivo PEC biosensing in deep tissue is seriously hampered because of the shallow penetration depth of ultraviolet and visible light. Expanding the optical absorption wavelength of photoelectrodes from the visible light region into the near-infrared (NIR) light region is highly desirable because of its deep tissue penetrability and minimal invasiveness for organisms, but the exploration of the facile strategy to implement efficient NIR absorption with good biocompatibility is still challenging. Herein, a NIR PEC aptasensor is proposed by coupling plasmonic nanoparticles (NPs) into periodic two-dimensional nanocavity (NC) photonic crystals as photoelectrodes, where the Au NPs are sputtered on a periodic two-dimensional TiO₂ NC photonic crystal substrate to significantly enhance the NIR PEC response and successfully achieve sensitive PEC detection of Hg²⁺ under irradiation of NIR light in blood. We believe that the proposed NIR-responsive Au/TiO₂ NC-based PEC aptasensor will open a new in vivo biosensing model for a series of important biomolecules and pave up an avenue for the practical applications of PEC biosensing in deep tissue or even in organs and brain of the living body.

Synergistic bio-recognition/spatial-confinement for effective capture and sensitive photoelectrochemical detection of MCF-7 cells

A synergistic bio-recognition/spatial-confinement strategy is proposed for the effective capture of cancer cells and sensitive photoelectrochemical detection with the lowest limit of detection of 2 cells per mL.