Recent Advances in Construction Strategies for Fluorescence Sensing Films

A year ago, film-based fluorescent sensors (FFSs) were recognized in the "IUPAC Top Ten Emerging Technologies in Chemistry 2022" due to their extensive application in detecting hidden explosives, illicit drugs, and volatile organic compounds. These sensors offer high sensitivity, specificity, immunity to light scattering, and noninvasiveness. The core of FFSs is the construction of high-performance fluorescent sensing films, which are dependent on the processes of "energy transfer" and "mass transfer" in the active layer and involve complex interactions between sensing molecules and analytes. This Perspective focuses on the latest strategies in constructing these films, emphasizing the design of sensing molecules with various innovative features and structures that enhance the mass transfer efficiency. Additionally, it discusses the ongoing challenges and potential advancements in the field of FFSs.

A Benzil- and BODIPY-Based Turn-On Fluorescent Probe for Detection of Hydrogen Peroxide

Faced with rising threats of terrorism, environmental and health risks, achieving sensitive and selective detection of peroxide-based explosives (PEs) has become a global focus. In this study, a turn-on fluorescent probe (BOD) based on benzil (H2O2-recognition element) and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivative (fluorophore) was developed to sensitively and specifically detect hydrogen peroxide (H2O2). The synthesized BOD had a very weak fluorescence due to intramolecular donor-excited photo-induced electron transfer (d-PET) effect; however, it could emit a strong fluorescence since H2O2 selectively oxidized the benzil moiety and released free BODIPY fluorophore (BOD-COOH). As a result, the proposed BOD detected H2O2 in linear detection ranged from 25 to 125 µM with a detection limit of 4.41 µM. Meanwhile, the proposed BOD showed good selectivity toward H2O2, which is not affected by other common reactive oxygen species (ROS) and ions from explosive residues. In addition, a blue shift from 508 to 498 nm was observed in the absorption spectra upon addition of H2O2. More importantly, the BOD was successfully applied for rapid detection of H2O2 vapor with good sensitivity (down to 7 ppb), which holds great potential for practical use in public safety, forensic analysis and environmental monitoring.

Recent development and trends in the detection of peroxide-based explosives

Peroxide-based explosives (PBEs) are increasingly common in criminal and terrorist activity due to their easy synthesis and high explosive power. The rise in terrorist attacks involving PBEs has heightened the importance of detecting trace amounts of explosive residue or vapors. This paper aims to provide a review on the developments of techniques and instruments for detecting PBEs over the past ten years, specifically discussing advancements in ion mobility spectrometry, ambient mass spectrometry, fluorescence techniques, colorimetric methods, and electrochemical methods. We provide examples to illustrate their evolution and focus on new strategies for improving detection performance, specifically in terms of sensitivity, selectivity, high-throughput, and wide explosives coverage. Finally, we discuss future prospects for PBE detection. It is hoped this treatment will serve as a guide to the novitiate and as aid memoire to the researchers.

Iodine-mediated photoinduced autoinductive tandem chromogenic system for visual colorimetric detection of triacetone triperoxide explosive

A long-standing challenge in colorimetric detection of triacetone triperoxide (TATP) explosive is low sensitivity. We herein developed an iodine-mediated photoinduced auto-inductive tandem chromogenic system to achieve exponential signal amplification. The strategy employs the KI-TATP reaction and photo-induced autocatalytical oxidation of o-phenylenediamine (OPD) that work in tandem. The resulting I₃^- from the KI-TATP reaction oxidizes OPD to yellow 2,3-diaminophenazine (DAP) that is further excited by blue light illumination to produce reactive oxygen species (ROS). The obtained ROS, in turn, promotes the oxidation of OPD to gain more DAP, causing the auto-inductive chromogenic reaction processes. This tandem chromogenic system is applied for visual colorimetric detection of TATP, allowing the selective and sensitive detection of TATP down to 42.8 μM. Moreover, analyses of TATP in real samples are performed, and the satisfactory recovery results are achieved. Furthermore, a field detection kit is also developed.

In Situ Turn-On Room Temperature Phosphorescence and Vapor Ultra-sensitivity at Lifetime Mode

Organic room temperature phosphorescence (RTP) systems are rarely reported for vapor phase sensing due to the contradiction between vapor permeability and phosphorescence ability. Till now, almost all reported works are based on ″turn-off″ mode RTP detection by destroying the compact-packaging oxygen-free environment. ″Turn-on″ mode RTP detection owns additional anti-interference capability due to a lower initial RTP background signal, while its realization is even harder. In this research, in situ phosphorescence ″turn-on″ sensing was realized for methamphetamine (MPEA) vapor detection. Based on the formation of aromatic phenolic aldehyde-secondary amine ion pairs with air-stable RTP performance, the fluorescent tri-formyl phenol (TFP) film was converted into a stable RTP state after being exposed to the MPEA vapor, as supported by nuclear magnetic resonance (NMR) and mass spectrometry together with theoretical calculations. The red-shifted absorption and emission, enhanced emission intensity, and 49.7 μs phosphorescence lifetime allowed multiple mode MPEA vapor sensing from chromaticity to fluorescence to phosphorescence. The lifetime mode detection limit reached 0.4 ppt, 5 orders of magnitude lower than the intensity mode detection limit of 20.3 ppb.

Selective dual detection of Hg2+ and TATP based on amphiphilic conjugated polythiophene-quantum dot hybrid materials

The design of multifunctional sensors based on biocompatible hybrid materials consisting of conjugated polythiophene-quantum dots for multiple environmental pollutants is a promising strategy for the development of new monitoring technologies. Herein, we present a new approach for the "on-off-on" sensing of Hg²⁺ and triacetone triperoxide (TATP) based on amphiphilic polythiophene-coated CdTe QDs (PQDs, PLQY ∼78%). The emission of the PQDs is quenched by Hg²⁺ ions via electron transfer interactions. Based on the strong interaction between TATP and Hg²⁺ ions, the addition of TATP to the PQD-Hg²⁺ complex results in a remarkable recovery of the PQD emission. Under the optimized conditions, the PQD sensor shows a good linear response to Hg²⁺ and TATP with detection limits of 7.4 nM and 0.055 mg L^-1, respectively. Furthermore, the "on-off-on" sensor demonstrates good biocompatibility, high stability, and excellent selectivity in the presence of other metal ions and common explosives. Importantly, the proposed method can be used to determine the level of Hg²⁺ and TATP in environmental water samples.

Recent Developments in the Field of Explosive Trace Detection

Explosive trace detection (ETD) technologies play a vital role in maintaining national security. ETD remains an active research area with many analytical techniques in operational use. This review details the latest advances in animal olfactory, ion mobility spectrometry (IMS), and Raman and colorimetric detection methods. Developments in optical, biological, electrochemical, mass, and thermal sensors are also covered in addition to the use of nanomaterials technology. Commercially available systems are presented as examples of current detection capabilities and as benchmarks for improvement. Attention is also drawn to recent collaborative projects involving government, academia, and industry to highlight the emergence of multimodal screening approaches and applications. The objective of the review is to provide a comprehensive overview of ETD by highlighting challenges in ETD and providing an understanding of the principles, advantages, and limitations of each technology and relating this to current systems.

A Facilely Synthesized Dual-State Emission Platform for Picric Acid Detection and Latent Fingerprint Visualization

To achieve a highly efficient, dual-state emission platform for picric acid (PA) detection and latent fingerprint (LFP) visualization, flexible alkyl chains have been facilely attached to the commercial organic dye 3,4,9,10-perylenetetracarboxylic dianhydride to provide the target perylenetetracarboxylate molecules PTCA-C4, PTCA-C6, and PTCA-C12. Interestingly, all these molecules exhibited impressive fluorescence characteristics with high photoluminescence quantum yields (PLQYs) of around 93.0 % in dilute solution. Also, emissive features were observed in the solid state because close molecular packing is prevented by the alkyl chains, especially for PTCA-C6, which has a high PLQY value of 49.0 %. Benefiting from its impressive fluorescence performance in both solution and as aggregates, PTCA-C6 was used as a dual-state emission platform for PA detection and also LFP visualization. For example, double-responsive fluorescence quenching in solution was observed in PA detection studies, resulting in high quenching constants (K_SV ) and also low limit-of-detection values. Furthermore, the fingerprint powder based on PTCA-C6 also presented an impressive performance on various substrates in terms of fluorescence intensity and resolution, clearly providing the specific fine details of latent fingerprints. These results demonstrate that the facilely synthesized PTCA-C6 with efficient dual-state emission exhibits great potential in the real-world applications of PA detection and LFP visualization.

Detection of hydrogen peroxide using dioxazaborocanes: elucidation of the sensing mechanism at the molecular level by NMR and XPS measurements

The H₂O₂vapour cleaves the N–B bond and inhibits the fluorescence of the dixazaborocane.

Fast, sensitive, selective and reversible fluorescence monitoring of TATP in a vapor phase

The development of sensors for the detection of triacetone triperoxide (TATP) has attracted great attention. Here, we constructed a low-cost, portable, reusable, visible paper-based fluorescent sensor for the sensitive detection of TATP via vapor sampling. Under optimized conditions, the fluorescent film showed a high sensitivity to TATP with a detection limit of lower than 0.5 μg mL-1 in air. The linear range of the response is from 0.5 to 8.0 μg mL-1. In addition, the paper-based sensor exhibited high selectivity to TATP. The presence of potential interferents showed little effect on sensing. Moreover, sensing is fully reversible. Fortunately, the test can also be conducted in a visualized way.

Handy fluorescent paper device based on a curcumin derivative for ultrafast detection of peroxide-based explosives

A useful and inexpensive fluorescent paper-based device was fabricated for ultrafast sensing of peroxide-based explosives.

Sorbent Film-Coated Passive Samplers for Explosives Vapour Detection Part A: Materials Optimisation and Integration with Analytical Technologies

A new thin-film passive sampler is presented as a low resource dependent and discrete continuous monitoring solution for explosives-related vapours. Using 15 mid-high vapour pressure explosives-related compounds as probes, combinations of four thermally stable substrates and six film-based sorbents were evaluated. Meta-aramid and phenylene oxide-based materials showed the best recoveries from small voids (~70%). Analysis was performed using liquid chromatography-high resolution accurate mass spectrometry which also enabled tentative identification of new targets from the acquired data. Preliminary uptake kinetics experiments revealed plateau concentrations on the device were reached between 3–5 days. Compounds used in improvised explosive devices, such as triacetone triperoxide, were detected within 1 hour and were stably retained by the sampler for up to 7 days. Sampler performance was consistent for 22 months after manufacture. Lastly, its direct integration with currently in-service explosives screening equipment including ion mobility spectrometry and thermal desorption mass spectrometry is presented. Following exposure to several open environments and targeted interferences, sampler performance was subsequently assessed and potential interferences identified. High-security building and area monitoring for concealed explosives using such cost-effective and discrete passive samplers can add extra assurance to search routines while minimising any additional burden on personnel or everyday site operation.

One step synthesis of silane-capped copper clusters as a sensitive optical probe and efficient catalyst for reversible color switching

Luminescent silane-functionalized copper clusters are developed as a highly efficient catalyst to build up a recyclable and photoreversible color switching system based on the redox reactions of methylene blue.