Detection Of Environmental Pollutants Research Articles

Titanium Mxene: A Promising Material for Next‐Generation Optical Biosensors and Machine Learning Integration

AbstractNano biosensors based on MXenes have been emerging as a promising tool in the detection of biomarkers, for the discrimination of diseases and in the detection of environmental pollutants. Their potential in sensing applications has also drawn a lot of attention to their unique qualities such as their high conductivity, huge surface area, outstanding hydrophilicity, biocompatibility, and simplicity of surface functionalization. The development of scalable synthesis techniques is essential to the large‐scale manufacturing and broad application of MXene‐based sensors. Furthermore, the stability of the MXene layers in diverse environmental circumstances continues to be a difficulty for their practical application. To increase the dependability and precision of MXene‐based sensors, their selectivity must be increased through functionalization and tuning. With innovative technologies like machine learning, MXene biosensor is now taken advantage of new opportunities. Personalized healthcare solutions, remote data analysis, and real‐time monitoring are all possible when MXene sensors and AI algorithms work together. Herein, the optical properties, synthesis approaches, role of MXene biosensors in machine learning, its significant challenges and future prospects of MXene‐based nano(bio)sensors are deliberated.

A Multifunctional Tb(III)-Based Metal-Organic Framework for Chemical Conversion of CO2, Fluorescence Sensing of Trace Water and Metamitron.

The utilization of metal-organic frameworks (MOFs) as fluorescent sensors for the detection of environmental and chemical reagent pollutants as well as heterogeneous catalysis for CO2 conversion represents a crucial avenue of research with significant implications for the protection of human health. In this work, a Tb(III)-based three-dimensional metal-organic framework, [Tb(L)·4DMF]n (Tb-MOF) (H3L = 5'-(4-carboxy-3-hydroxyphenyl)-3,3″-dihydroxy-[1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid), has been structurally conformed by single-crystal X-ray crystallography. It possesses a 1D rhombus channel along the [010] direction, featuring a pore size of 6.02 × 9.13 Å. Tb-MOF was proved to be a multifunctional material for a fluorescent sensor and CO2 cycloaddition heterogeneous catalyst material. Fluorescence sensing studies revealed that Tb-MOF demonstrates high sensitivity, selectivity, and favorable regeneration properties, making it an effective chemosensor for detecting the metamitron (MMT) pesticide and trace water in organic solvents. The mechanism of fluorescence quenching by MMT and water was elucidated by a combination of XRD, UV-vis absorption spectra, IR spectra, theoretical calculations, and fluorescence lifetimes. The material was also utilized for the sensing of MMT and water in paper strips. Additionally, the open Tb3+ site as Lewis acidic centers makes Tb-MOF achieve efficiently catalytic conversion for CO2 and epoxides to cyclic carbonates. Moreover, a possible catalytic mechanism for the conversion of carbon dioxide to cyclic carbonates was proposed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments. It also exhibited recyclability for up to five cycles without noticing an appreciable loss in sensing or catalytic efficiency.

Copper@MXene quantum dots-aerogel: High-performance peroxidase mimic for direct pirimiphos-methyl pesticide detection

Due to their cost-efficiency and heightened sensitivity, the rational design of artificial nanozymes has become a paramount research direction. In this investigation, we elaborate on a simplified freeze-drying methodology for fabricating Cu@MXene quantum dots-aerogel (Cu@MQDs-aerogel), which possesses augmented peroxidase-mimicking activity. Through steady-state fluorometric analysis, we delve into the catalytic mechanism of Cu@MQDs-aerogel, uncovering its proficiency in decomposing H2O2 into reactive hydroxyl radicals (OH). Density functional theory (DFT) calculations further validate that the outstanding catalytic prowess of Cu@MQDs-aerogel stems from the interfacial Cu-Ti dimer active sites, significantly activating adsorbed H2O2 and facilitating its decomposition into OH. As a result, we introduce a sensitive colorimetric sensor for pirimiphos-methyl detection, achieving a low detection limit of 0.65 nM. Additionally, it exhibits a narrow relative standard deviation (RSD) interval spanning from 1.03 % to 2.66 %. This study introduces a novel strategy for the design and synthesis of MQDs-based peroxidase-like enzymes, highlighting their significant potential in environmental pollutant detection.

Aqua Quadcopter an Engineering Solution for Water Sample Collection

An “Aqua Quadcopter” designed for water sample collection is a specialized quadcopter capable of flying over water bodies and collecting water samples for analysis. This type of drone combines aerial mobility with aquatic capabilities, making it suitable for environmental monitoring, scientific research, and pollution detection in rivers, lakes, oceans, and other water bodies. Traditional methods of water sample collection are often labour- intensive, time consuming, and may require boats or human intervention in potentially hazardous environments. This project addresses the need for a more efficient, safer, and autonomous solution that can access remote or hard-to-reach areas and provide real-time data for environmental analysis. We are going to design drone and water sampler, adding some specifications like GPS system to target the area where it is polluted and observe the stability of quadcopter.

A simple, rapid, and low-cost approach for colloidal nanoparticle-based surface enhanced Raman Scattering detection of endosulfan pesticide at trace levels

Abstract Surface Enhanced Raman Spectroscopy (SERS) is a highly specific, sensitive, and portable technique with great potential for on-site pesticide detection and monitoring. Endosulfan, an organochlorine pesticide known for its high toxicity, slow degradation, and bioaccumulation, has poor affinity for metallic SERS substrates. This study presents a label-free SERS detection method for endosulfan, using aggregating agents like potassium chloride (KCl), potassium hydroxide (KOH), potassium bromide (KBr), and sodium hydroxide (NaOH) to modify the behavior of Ag colloidal nanoparticles (NPs) and enhance the SERS signal of endosulfan molecules trapped within formed hot-spots. We analyzed the UV–Vis spectra, the hydrodynamic diameter, and zeta-potential of Ag NPs with the addition of these agents and endosulfan. Successful detection of both α- and ß- endosulfan isomers at μM concentrations in both ethanol and methanol was achieved with KOH-treated Ag NPs. The method was also applied to detect endosulfan in real water samples, along with simultaneous detection of λ-cyhalothrin, showcasing its capability to identify multiple analytes. The selectivity and specificity were confirmed using a mixture of endosulfan and thiabendazole, highlighting the crucial role of selecting the appropriate aggregating agent for each analyte. Overall, the findings emphasize the potential of aggregating agents to mediate the SERS enhancement of endosulfan, facilitating simple and rapid protocols for environmental pollutant detection, while shedding light on the intricate interplay between NP behavior, surface chemistry, and analyte interaction.

Reaction-Based SERS Probes for the Detection of Raman-Inactive Species.

Surface-enhanced Raman spectroscopy (SERS) has the advantages of high sensitivity, low water interference, narrow spectral peaks for multicomponent analysis, and rich molecular fingerprint information, presenting great potential to be a robust analytical technology. However, a key issue is the unavailability in directly detecting Raman-inactive species with a small Raman scattering cross-section. Current research has addressed this issue by using specific chemical reactions to induce significant characteristic changes in SERS signals, enabling the sensitive and selective detection of Raman-inactive species. This reaction-activated SERS sensing strategy provides a clever approach to the precise determination of Raman-inactive species. In this review, we have first summarized the design principles and types of reaction-based SERS probes. Furthermore, we have examined the enormous potential of reaction-based SERS probes in the detection of bioactive species, environmental pollutants, and food contaminants. Finally, we have discussed in depth the challenges and prospects of reaction-based SERS probes on stability, reliability, and intelligence. The review is aimed to inspire a more advanced design of reaction-based SERS probes, thus further facilitating their extensive applications in SERS analysis.

Eu-doped carbon dots-MOF based turn-on fluorescent probe for trace Hg2+ and Pb2+ and construction of the simultaneous detection model

Multiple trace heavy metal pollutants present a serious threat to the aquatic environment, and their coexistence also affected the detection efficiency. This work prepared Eu doped metal organic framework (MOF) complexed with S-containing carbon dots (CD(s)) exhibited dual-emission fluorescence. Its chelation-enhanced fluorescence with heavy metals replaced the original agglomerative fluorescence quenching of pure CD(s), which was utilized to construct a “turn on” fluorescence sensing probe. Based on the XPS, DFT and fluorescence lifetime results, the N, S functional groups on the surface of the materials could bind specifically to Hg2+ and Pb2+ with enhanced sensitivity. The limit of detection reached 76.67 nM for Hg2+ and 5.12 nM for Pb2+ within 2 min detection time. Furthermore, due to the different response mechanism of the two signal peaks to Hg2+ and Pb2+, a three-dimensional data model was developed for simultaneous detection in the co-existence system. The model had been successfully applied to actual Hg2+-Pb2+ containing water samples with recoveries ranged from 93.15 ∼ 105.08 %. The results provided a new strategy for simultaneous detection of trace environmental pollutants.

Understanding the gas sensing mechanism of MoSe2 nanoroses and rGO composite-based chemiresistive sensors for room temperature NO2 detection

This study presents the synthesis of single-phase 2H-MoSe2 and one-pot synthesis of MoSe2/rGO (MSR) composite used for the detection of environmental pollutants (NO2, NH3, H2S CO2, CO, CH4, CH3COCH3) at ambient temperature (∼25 °C). The gas sensing devices were fabricated on Ti/Pt interdigitated electrodes with different compositions of MSR composite viz. 10 (MSR-10), 20 (MSR-20), and 30 (MSR-30) weight % of rGO. The sensitivity of the p-type MoSe2, rGO and MSR-20 was calculated to be ∼29 %, ∼24 % & ∼38 %, respectively at 4 ppm concentration of NO2. The respective response and recovery time were calculated to be 191/218 s, 225/412 s, and 110/128 s for MoSe2, rGO, and MSR-20 composite at 4 ppm of NO2 gas. The response curve at the lowest detection limit indicates stable performance of the device, which makes it suitable for its real-time application. The response time and recovery time of the composite device are 40 s and 65 s, respectively at 100 ppb concentration of NO2 gas. The sensing device was subjected to 0.1 ppm to 4 ppm of NO2 gas concentration, and the obtained device response was highly repeatable and stable after 60 days. The possible gas sensing mechanism based on charge transfer is proposed for fabricated devices using MSR composite material. The gas sensing device parameters, selectivity, repeatability, sensitivity, and stability show a great potential of MoSe2-rGO composite material in gas sensing.

Convenient Au@Ag Double‐Layer Nanoarray Fabricated by Rapid Thermal Annealing and Chemical Replacement Method for Surface‐Enhanced Raman Spectroscopy Sensing

Surface‐enhanced Raman spectroscopy (SERS) has a wide range of applications in molecular recognition, environmental pollutant detection, and other fields. However, the intensity and number of “hot spots” in 1D and 2D nanostructures are limited due to the scale‐dependent localized plasmonic effect of nanostructures, making it difficult to increase the detection limit. Herein, a kind of 3D substrate called Au@Ag double‐layer nanoarray (Au@Ag DLA) is prepared using rapid thermal annealing and chemical replacement methods. The energy‐dispersive spectrometer spectra confirm the successful growth of AgNPs on the gold nanoarray (Au SLA) by showing no presence of the copper element, indicating complete replacement of the Cu film deposited on Au SLA by Ag atoms. The detection limit of malachite green in Au@Ag DLA is 10−8 mol L−1, four and three orders of magnitude higher than that of Au SLA and AgNPs, respectively. This stronger SERS effect of Au@Ag DLA arises from the larger number of intense hot spots generated not only on the horizontal surface but also in the vertical direction. This finding provides a method for developing efficient and stable 3D SERS substrate, which can be utilized for the trace detection of water pollutants and pesticide residue.

Surface-Enhanced Raman Scattering Spectroscopy: An Effective Tool for the Detection of Environmental Pollutants

Surface-Enhanced Raman Scattering Spectroscopy: An Effective Tool for the Detection of Environmental Pollutants

An electrochemical sensor based on the molecularly imprinted polymer/ single walled carbon nanotube-modified glassy carbon electrode for detection of zineb fungicide in food samples

In the present study, a selective electrochemical technique to determine Zineb fungicide based on molecularly imprinted polymer (MIP) as a simple and fast method was developed. The MIP was synthesized on a glassy carbon electrode (GCE) modified with single walled carbon nanotube (SWCNT) through electropolymerization of ortho-aminophenol (o-AP) monomer and Zineb fungicide analyte. Some ions and compounds were examined as the interfering species to investigate the selectivity of the developed sensor. This research proposes simple determination of Zineb fungicide with a linear range 5–1000 fM and limit of detection (LOD) 1.6 fM. Finally, this strategy was successfully used to detect Zineb in some vegetable and fruit samples such as cucumber, potato, tomato, lettuce, peach, and apple with a satisfactory recovery range between 98.85 and 102.00%. The obtained results indicated that the newly developed method is stable, convenient, and has easy preparation steps with low-cost materials. It can be used for rapid diagnosis of Zineb in crops and agriculture products, which holds great promise in detection of environmental pollutants.

Reaction Time Induced a Two-Step Dissolution and Recrystallization Structural Transformation with Three Eu Metal-Organic Frameworks: Crystal Structures and Multiresponsive Fluorescence Detection.

Under solvothermal conditions, three 3D lanthanide metal-organic frameworks (Ln-MOFs): [Eu(H2DHTA)1.5(DMF)2]·DMF (1), [Eu(H2DHTA)0.5(DHTA)0.5(DMF)(H2O)]·2H2O (2), and Eu(HCOO)3 (3) (H4DHTA = 2,5-dihydroxyterephthalic acid) have been synthesized by different reaction times. Interestingly, induced by reaction time, compounds 1-3 underwent a two-step dissolution and recrystallization structural transformation (DRST) reaction. Investigations on the DRST processes were carried out, and the transformation pathway was deduced, which was verified by XRD analyses. Notably, compound 2 demonstrates pronounced luminescence as well as high stability in water and other organic solvents. The fluorescent detection of furan antibiotics can serve as turn-off effects, and glutamic acid (Glu), aspartic acid (Asp), and riboflavin (VB2) can serve as the turn-on effect. To explain the enhancing and quenching mechanisms, XRD, UV-visible absorption spectroscopy, electrochemistry, IR spectra, theoretical calculation, fluorescence lifetimes, and XPS were discussed. Additionally, MOF-coated test strips were utilized to detect these analytes, exhibiting excellent agreement with fluorescence spectroscopy. This work provides an example for more effective designs to employ Ln-MOFs as multiresponsive fluorescent sensors for detection of environmental pollutants in aqueous solution.

Application of Ionic Liquids in Environmental and Food Fields

Abstract: As a new type of green solvent, ionic liquids have made rapid progress in the fields of organic synthesis, separation, and electrochemistry due to their unique physical and chemical properties. At the same time, the new fluorescence characteristics and good separation and adsorption functions of ionic liquids have gradually developed in the field of environment and food, showing a good application prospect. Based on the work of our research group and the progress and development of research technology, this article reviews the research results of ionic liquids in environmental monitoring and food detection and extraction in recent years. In the environmental field, ionic liquids have the ability of detection and remediation and they show the advantages of fast, efficient, green and recyclable in the detection of environmental pollutants. In the field of food, ionic liquids provide a new idea for the detection and extraction technology of food components. While ensuring green, safe and pollution-free, they show superior selectivity, repeatability and stability, and simplify the operation steps and costs to a certain extent, showing the capture vitality with life characteristics. As a potential smart material, the mechanism of ionic liquids as fluorescent probes and separation extractants was discussed. Finally, the future development and research directions of ionic liquids are prospected, and it is expected to realize the intelligentization of ionic liquid materials and the general integration of development.

Graphene-Liquid Crystal Synergy: Advancing Sensor Technologies across Multiple Domains.

This review explores the integration of graphene and liquid crystals to advance sensor technologies across multiple domains, with a focus on recent developments in thermal and infrared sensing, flexible actuators, chemical and biological detection, and environmental monitoring systems. The synergy between graphene's exceptional electrical, optical, and thermal properties and the dynamic behavior of liquid crystals leads to sensors with significantly enhanced sensitivity, selectivity, and versatility. Notable contributions of this review include highlighting key advancements such as graphene-doped liquid crystal IR detectors, shape-memory polymers for flexible actuators, and composite hydrogels for environmental pollutant detection. Additionally, this review addresses ongoing challenges in scalability and integration, providing insights into current research efforts aimed at overcoming these obstacles. The potential for multi-modal sensing, self-powered devices, and AI integration is discussed, suggesting a transformative impact of these composite sensors on various sectors, including health, environmental monitoring, and technology. This review demonstrates how the fusion of graphene and liquid crystals is pushing the boundaries of sensor technology, offering more sensitive, adaptable, and innovative solutions to global challenges.

A multi-dimensional anti-counterfeiting nanocomposite based on fluorescent CDs and Eu-MOFs with dual function for continuous detection of Cu2+ and Bacillus anthracis

Traditional luminescent materials for anti-counterfeiting usually adopt encryption of low-level systems with limited security, which seriously hinders their application in preventing counterfeiting and information leakage. Therefore, it is urgent to develop materials for higher-level anti-counterfeiting. In this work, a stimulus-responsive intelligent luminescent material (AC@CDs-Eu-MOFs) was prepared by co-loading green-fluorescence CDs and red-fluorescence Eu-MOFs on Amino clay (AC). 5D security barcodes, which were easy to observe while difficult to clone, were ulteriorly designed based on the nanocomposite owing to the tunable fluorescence by optical stimulation and chemical stimulus. Owing to the large capacity, low cost, and easy authentication, the 5D security barcodes possess enormous potential in optical data storage and multi-dimensional information encryption. In addition, the chemical stimulus-response enables the nanocomposite achievable in detection of Cu2+ and Bacillus anthracis. Particularly, quantitative determination of copper in environmental water samples could be realized with a detection limit as low as 10.67 nM. Therefore, the material shows potential for detection of environmental pollutants besides advanced anti-counterfeiting.

Recent advances in MXene nanomaterials: Fundamentals to applications in environment sector

AbstractMXenes are a new type of 2D transition metal carbon/nitride or carbonitride, which are composed of Mn+1AXn phase material (MAX phase) through single‐layer or thin‐layer nanosheets obtained by exfoliation. Owning to unique two‐dimensional layered structure, large specific surface area, excellent electrical conductivity and mechanical stability, the MXenes have quickly become a research hotspot due to their magnetic and other properties, and have been widely used in many fields such as electrochemical sensors, energy storage, catalysis, and adsorption. This article summarizes and introduces preparation methods of two‐dimensional materials MXenes, and focus on reviewing their application research progress in the electrochemical sensors and environmental field in recent years, including detection of biomarkers and environmental pollutants, adsorption of heavy metals, adsorption of radiation metals, adsorption of organic matter, selective adsorption of carbon dioxide, membrane separation, sensors, electrocatalysis, photocatalysis, electromagnetic absorption and shielding, etc. A summary and review were conducted, and finally the existing problems and future development at this stage were analyzed.

Phosphomolybdates for Dual-Mode Photoelectrochemical Sensing toward Trace Chromium(VI) and Tetracycline.

Highly sensitive photoelectrochemical (PEC) sensors for trace carcinogens, such as heavy metal chromium(VI) [Cr(VI)] and antibiotic tetracycline (TC) are crucial. Herein, by integration of photoactive and redox phosphomolybdates with conjugated organic components, types of dual-mode PEC sensors were synthesized for sensing trace Cr(VI) and TC pollutants, with formulas of (H2bimb)2[Co2(bimb)1.5][Co(H2O)4][Co(P4Mo6O31H6)2]·6H2O (1), (H2bib)2[Co(H2O)3][Co2(H2O)5][Co(P4Mo6O31H6)2]·9H2O (2), and (H2bib)6[Co(Hbib)2(H2O)5][Co(P4Mo6O31H7)2]2·15H2O (3), where bimb represents 1,4-bis(1-imidazolyl)benzene and bib is 4,4'-bis(imidazolyl)bibphenyl. Hybrid 1 consisted of a three-dimensional framework structure constructed by Co{P4Mo6}2 clusters and one-dimensional (1D) {Co-bimb} chains, hybrid 2 exhibited 1D Co ion-bridged Co{P4Mo6}2 chains hydrogen-bonding with [H2bib]2+ cations, and hybrid 3 showed a discrete hybrid structure built upon a Co{P4Mo6}2 cluster modified by the {Co-bib} unit. Hybrids 1-3 displayed wide spectral absorption and excellent electrochemical redox properties, enabling dual-mode PEC responses to Cr(VI) reduction and TC oxidation. For Cr(VI) detection, hybrids 1-3 exhibited high sensitivities of 364.40, 225.72, and 124.29 μA·μM-1 as well as "nM" level detection limits (LODs) of 4.9, 10.0, and 11.0 nM, respectively. For TC detection, the sensitivities of hybrids 1-3 were 494.72, 308.78, and 174.03 μA·μM-1 and the LODs were 5.2, 6.1, and 12.9 nM, respectively. This research offers significant insights into designing efficient PEC sensors for the detection of environmental pollutants.

On-site sensing for aflatoxicosis poisoning via ultraviolet excitable aptasensor based on fluorinated ethylene propylene strip: a promising forensic tool

The environmental contamination by extremophile Aspergillus species, i.e., Aflatoxin B1, is hardly controllable in Southeast Asia and Sub-Saharan Africa, which lack handling resources and controlled storage facilities. Acute aflatoxicosis poisoning from aflatoxin-prone dietary staples could cause acute hepatic necrosis, acute liver failure, and death. Here, as the cheaper, more straightforward, and facile on-site diagnostic kit is needed, we report an ultraviolet-excitable optical aptasensor based on a fluorinated ethylene propylene film strip. Molecular dynamics on the aptamer.AFB1 complex revealed that the AFB1 to the aptamer increases the overall structural stability, suggesting that the aptamer design is suitable for the intended application. Under various influencing factors, the proposed label-free strategy offers a fast 20-min on-site fabrication simplicity and 19-day shelf-life. The one-pot incubation provides an alternative to catalytic detection and exhibited 4 times reusability. The recovery of crude brown sugar, processed peanuts, and long-grain rice were 102.74 ± 0.41 (n = 3), 86.90 ± 3.38 (n = 3), and 98.50 ± 0.42 (n = 3), comparable to High-Performance Liquid Chromatography-Photodiode Array Detector results. This study is novel owing to the peculiar UV-active spectrum fingerprint and the convenient use of hydrophobic film strips that could promote breakthrough innovations and new frontiers for on-site/forensic detection of environmental pollutants.

Enhanced Fluorescence Based on Slow Light Effect of ZIF-8 Photonic Crystals for Trace 2,4,6-Trinitrophenol Detection.

In response to growing concerns about public safety and environmental conservation, it is essential to develop a precise identification method for trace explosives. To improve the stability and detection sensitivity of perovskite quantum dots (PQDs) and address the issue of low porosity in traditional polymer-based photonic crystals (PhCs), this study proposed a PQD photoluminescence (PL) enhancement strategy based on the slow light effect of ZIF-8 PhCs for highly sensitive, selective, and convenient detection of 2,4,6-trinitrophenol (TNP). The slow light effect at the photonic band gap edge is the basis of amplifying the PL signal. PhCs were fabricated by the evaporation-induced self-assembly method. The diffraction wavelength overlapping the whole visible region was designed to match the emission wavelength of PQDs. Results showed that PhCs matching the PBG edge with PQDs' emission peak amplified the PL signal 11.3 times, significantly improving sensitivity for trace TNP detection with a limit as low as 2.52 nM. Moreover, there was a 13.3-fold enhancement of PQDs' fluorescence lifetime when the emission wavelength fell in the PBG range. The hydrophobic surface of ZIF-8 PhCs enhanced the PQDs' stability and moisture resistance. Furthermore, the selective quenching mechanism of TNP by the sensor was photoinduced electron transfer (PET) verified by DFT calculations and time-resolved PL decay dynamics measurements. This study demonstrated great potential for manipulating light emission enhancement by PhCs in developing efficient fluorescent sensors for trace environmental pollutant detection.

Aptamer molecular gate functionalized mesoporous SiO2@MB controlled-release system for pollutant detection using Ti(Ⅲ) self-doped TiO2 NTs as active photoanode coupled with electrostatic modulation

Atrazine (ATZ) is a widely used herbicide that can cause serious harm to organisms and ecosystems. An immobilization-free photoelectrochemical (PEC) aptasensor has been herein developed for ATZ based on aptamer molecular gate functionalized mesoporous SiO2@MB controlled release system. Compared with traditional immobilization-based sensors, immobilization-free sensors (IFSs) avoid the modification of the recognition element on the electrode surface. Mesoporous SiO2 with large surface area and good biocompatibility can be used as nanocontainers to stably encapsulate the signal shuttle molecule methylene blue (MB). The bifunctional aptamer (APT) is used not only as the recognition element for ATZ but also as the signal switch to block or release MB. In the presence of ATZ, the specific recognition between ATZ and APT will cause the detachment of APT from the surface of SiO2, thus the molecular gate will open and release MB. Due to pH modulation, the positively charged MB can reach the surface of the negatively charged Ti(III) self-doped TiO2 NTs (Ti(III)–TiO2 NTs) electrode to act as an electron donor, which increases the photocurrent. The immobilization-free aptasensor has shown ultrasensitive detection of ATZ with a wide linear range from 1.0 pM to 100.0 nM and a low detection limit of 0.1 pM. In addition, the sensor has excellent selectivity, stability and anti-interference ability, and has been used in real water sample analysis successfully. This strategy has provided a new idea for the design of advanced immobilization-free PEC sensors for environmental pollutant detection.