Colorimetric sensor arrays based on pattern recognition for the detection of nitroaromatic molecules

Colorimetric - Fluorescence - Photothermal tri-mode sensor array combining the machine learning method for the selective identification of sulfonylurea pesticides

Though cholinesterase-based method could detect two types of pesticides (organophosphorus and carbamate), they had weak sensing on sulfonylurea pesticides. In our previous work, the peroxidase-like reaction system of nanozyme - H2O2 - TMB showed selective detection of sulfonylurea pesticides, but the single-signal output sensing platform was easily affected by complex matrix background, cross-contamination and human error. Therefore, this work used colorimetric, photothermal, and fluorescent signals of the nanozyme reaction as sensing units for the detection of pesticides. This is the first time that photothermal signals have been used to construct a sensor array. When the concentration of interfering substances was 25 times that of pesticides, the method was still unaffected and had excellent selectivity and anti-interference performance. Meanwhile, a concentration-independent differentiation mode was established based on the K-nearest neighbor (KNN) algorithm. The pesticides were detected and distinguished with 100% accuracy. This work contributed to the detection of sulfonylurea pesticides in complex environmental/food matrices, bridging the gap of existing pesticide detection methods and providing an effective method for food safety detection.

Recent Developments in the Detection of Organic Contaminants Using Molecularly Imprinted Polymers Combined with Various Analytical Techniques

Molecularly imprinted polymers (MIPs) encompass a diverse array of polymeric matrices that exhibit the unique capacity to selectively identify a designated template molecule through specific chemical moieties. Thanks to their pivotal attributes, including exceptional selectivity, extended shelf stability, and other distinct characteristics, this class of compounds has garnered interest in the development of highly responsive sensor systems. As a result, the incorporation of MIPs in crafting distinctive sensors and analytical procedures tailored for specific analytes across various domains has increasingly become a common practice within contemporary analytical chemistry. Furthermore, the range of polymers amenable to MIP formulation significantly influences the potential utilization of both conventional and innovative analytical methodologies. This versatility expands the array of possibilities in which MIP-based sensing can be employed in recognition systems. The following review summarizes the notable progress achieved within the preceding seven-year period in employing MIP-based sensing techniques for analyte determination.

A multifunctional cucurbit[6]uril-based supramolecular assembly for fluorescence sensing of TNP and Ba2+ and information encryption

Both nitroaromatic compounds (NACs) and heavy metal ions are accumulative high-risk environmental pollutants, so high-sensitivity detection of these environment pollutants is necessary. In this work, a cucurbit[6]uril (CB[6]) based luminescent supramolecular assembly [Na₂K₂(CB[6])₂(DMF)₂(ANS)(H₂O)₄](1) (CB[6] = cucurbit[6]uril, ANS^2- = 8-Aminonaphthalene-1,3,6-trisulfonic acid ion) has been synthesized under solvothermal conditions, using ANS^2- as a structural inducer. Performance studies have shown that 1 exhibits excellent chemical stability and easy regeneration ability. It can highly selective sensing of 2,4,6-trinitrophenol (TNP) through fluorescence quenching with a strong quenching constant (K_sv = 2.58 × 10⁴ M^-1). Additionally, the fluorescence emission of 1 can be effectively enhanced with Ba²⁺ in aqueous solution (K_sv = 5.57 × 10³ M^-1). More impressively, Ba²⁺@1 was successfully used as anti-counterfeiting fluorescent ink functional material with strong information encryption function. This work illustrates the application prospects of luminescent CB[6]-based supramolecular assembly in environmental pollutants detection and information anti-counterfeiting for the first time, which extends the multifunctional application scope of CB[6]-based supramolecular assembly.

Fluorimetric identification of sulfonamides by carbon dots embedded photonic crystal molecularly imprinted sensor array

Identification of sulfonamides (SAs) residues in food is vital for human health. A set of 4-channel sensor array was constructed by carbon dots (CDs) embedded in photonic crystal molecularly imprinted (PCMIP@CDs) film which included 3 PCMIP@CDs units and 1 PCNIP@CDs unit to determine typical SAs: sulfadimethoxine, sulfathiazole, sulfaguanidine, sulfamethazine, sulfadiazine. Under the optimal conditions, the response time of the sensor array was only 200 s. Moreover, 300 fluorescence response signals (4 sensor units × 5 sulfonamides × 3 concentrations × 5 repeats) were processed by pattern recognition technique to analyze the ability of the sensor array to recognize 5 kinds of SAs. Subsequently, the linear discrimination analysis (LDA) method was used to identify the five SAs simultaneously with 100 % classification accuracy and the limit of detection was 0.01-0.26 nmol/L. Moreover, the proposed method can effectively identify-five SAs in water and fish samples.

Recent Progress in Sensor Arrays: From Construction Principles of Sensing Elements to Applications

The traditional sensors are designed based on the "lock-and-key" strategy with high selectivity and specificity for detecting specific analytes, which however are not suitable for detecting multiple analytes simultaneously. With the help of pattern recognition technologies, the sensor arrays excel in distinguishing subtle changes caused by multitarget analytes with similar structures in a complex system. To construct a sensor array, the multiple sensing elements are undoubtedly indispensable units that will selectively interact with targets to generate the unique "fingerprints" based on the distinct responses, enabling the identification among various analytes through pattern recognition methods. This comprehensive review mainly focuses on the construction strategies and principles of sensing elements, as well as the applications of sensor array for identification and detection of target analytes in a wide range of fields. Furthermore, the present challenges and further perspectives of sensor arrays are discussed in detail.

State-of-the-art molecular imprinted colorimetric sensors and their on-site inspecting applications

Molecular imprinted colorimetric sensors can realize visual semi-quantitative analysis without the use of any equipment. With the advantages of low cost, fast response, ease of handling, and excellent recognition ability, the molecular imprinted colorimetric sensor shows great application potential in the field of sample rapid assay. Molecular imprinted colorimetric sensors can be prepared in various forms to meet the needs of different sample determination, such as film, hydrogel, strip, and adsorption coating. In this review, the preparation methods for various types of molecularly imprinted colorimetric sensors are systematically introduced. Their applications in the field of on-site biological sample detection, drug detection, disease treatment, chiral substance detection and separation, environmental analysis, and food safety detection are introduced. The limitations encountered in the practical application are presented, and the future development directions prospect.

A Robust Method for the Elaboration of SiO2-Based Colloidal Crystals as a Template for Inverse Opal Structures

Photonic crystals (PCs) are nanomaterials with photonic properties made up of periodically modulated dielectric materials that reflect light between a wavelength range located in the photonic band gap. Colloidal PCs (C-PC) have been proposed for several applications such as optical platforms for the formation of physical, chemical, and biological sensors based on a chromatic response to an external stimulus. In this work, a robust protocol for the elaboration of photonic crystals based on SiO₂ particle (SP) deposition using the vertical lifting method was studied. A wide range of lifting speeds and particle suspension concentrations were investigated by evaluating the C-PC reflectance spectrum. Thinner and higher reflectance peaks were obtained with a decrease in the lifting speed and an increase in the SP concentrations up to certain values. Seven batches of twelve C-PCs employing a SP 3% suspension and a lifting speed of 0.28 µm/s were prepared to test the reproducibility of this method. Every C-PC fabricated in this assay has a wavelength peak in a range of 10 nm and a peak width lower than 90 nm. Inverse-opal polymeric films with a highly porous and interconnected morphology were obtained using the developed C-PC as a template. Overall, these results showed that reproducible colloidal crystals could be elaborated on a large scale with a simple apparatus in a short period, providing a step forward in the scale-up of the fabrication of photonic colloidal crystal and IO structures as those employed for the elaboration of photonic polymeric sensors.

Rapid quantification of acid value in frying oil using iron tetraphenylporphyrin fluorescent sensor coupled with density functional theory and multivariate analysis

Metalloporphyrin-based fluorescent sensor was developed for the acid value in frying oil. The electronic and structural performances of iron tetraphenylporphyrin (FeTPP) were theoretically investigated using time-dependent density functional theory (TD-DFT) and DFT at the B3LYP/LANL2DZ level. The quantified FeTPP-based fluorescent sensor results revealed its excellent performance in discriminating different analytes. In the present work, the acid value of palm olein was determined after every single frying cycle. A total of 10 frying cycles were conducted each day for 10 consecutive days. The FeTPP-based fluorescent sensor was used to quantify the acid value and the results were compared with the chemical data obtained by conventional titration method. The synchronous fluorescence spectrum for each sample was recorded. Parallel factor analysis (PARAFAC) was used to decompose the three-dimensional spectrum data. Then, the support vector regression (SVR), partial least squares (PLS), and back-propagation artificial neural network (BP-ANN) methods were applied to build the regression models. After the comparison of the constructed models, the SVR models exhibited the highest correlation coefficients among all models, with 0.9748 and 0.9276 for the training and test set, respectively. The findings suggested the potential of FeTPP-based fluorescent sensor in rapid monitoring of the used frying oil quality and perhaps also in other foods with higher oil content.

Identification of Two Commercial Pesticides by a Nanoparticle Gas-Sensing Array

This study presents the experimental testing of a gas-sensing array, for the detection of two commercially available pesticides (i.e., Chloract 48 EC and Nimrod), towards its eventual use along a commercial smart-farming system. The array is comprised of four distinctive sensing devices based on nanoparticles, each functionalized with a different gas-absorbing polymeric layer. As discussed herein, the sensing array is able to identify as well as quantify three gas-analytes, two pesticide solutions, and relative humidity, which acts as a reference analyte. All of the evaluation experiments were conducted in close to real-life conditions; specifically, the sensors response towards the three analytes was tested in three relative humidity backgrounds while the effect of temperature was also considered. The unique response patterns generated after the exposure of the sensing-array to the two gas-analytes were analyzed using the common statistical analysis tool Principal Component Analysis (PCA). The sensing array, being compact, low-cost, and highly sensitive, can be easily integrated with pre-existing crop-monitoring solutions. Given that there are limited reports for effective pesticide gas-sensing solutions, the proposed gas-sensing technology would significantly upgrade the added-value of the integrated system, providing it with unique advantages.

The Use of Computational Methods for the Development of Molecularly Imprinted Polymers

Recent years have witnessed a dramatic increase in the use of theoretical and computational approaches in the study and development of molecular imprinting systems. These tools are being used to either improve understanding of the mechanisms underlying the function of molecular imprinting systems or for the design of new systems. Here, we present an overview of the literature describing the application of theoretical and computational techniques to the different stages of the molecular imprinting process (pre-polymerization mixture, polymerization process and ligand-molecularly imprinted polymer rebinding), along with an analysis of trends within and the current status of this aspect of the molecular imprinting field.

Recent Advances in Sensing Applications of Molecularly Imprinted Photonic Crystals

Photonic crystals (PhCs) with a brightly colored structure are novel materials and are widely used in chemical and biological sensing. Combining PhCs with molecular imprinting technology (MIT), the molecularly imprinted PhC (MIPC) sensors are fabricated, which can specifically recognize the target molecules. Aside from high sensitivity and selectivity, the MIPC sensors could recognize the naked eye detection because of its optical properties. In this review, an overview of recent advances in sensing applications of MIPC sensors including the responsive mechanisms, application in environmental monitoring, and the application to human health were illustrated. The MIPC sensors all responded to the analytes specifically and also showed high sensitivity in real samples, which provided a method to realize the rapid, convenient, naked eye, and real-time detection. Furthermore, the current limitations and potential future directions of MIPC sensors were also discussed.

Molecularly Imprinted Polymer-Based Sensors for Priority Pollutants

Globally, there is growing concern about the health risks of water and air pollution. The U.S. Environmental Protection Agency (EPA) has developed a list of priority pollutants containing 129 different chemical compounds. All of these chemicals are of significant interest due to their serious health and safety issues. Permanent exposure to some concentrations of these chemicals can cause severe and irrecoverable health effects, which can be easily prevented by their early identification. Molecularly imprinted polymers (MIPs) offer great potential for selective adsorption of chemicals from water and air samples. These selective artificial bio(mimetic) receptors are promising candidates for modification of sensors, especially disposable sensors, due to their low-cost, long-term stability, ease of engineering, simplicity of production and their applicability for a wide range of targets. Herein, innovative strategies used to develop MIP-based sensors for EPA priority pollutants will be reviewed.

Wearable Biosensors: An Alternative and Practical Approach in Healthcare and Disease Monitoring

With the increasing prevalence of growing population, aging and chronic diseases continuously rising healthcare costs, the healthcare system is undergoing a vital transformation from the traditional hospital-centered system to an individual-centered system. Since the 20th century, wearable sensors are becoming widespread in healthcare and biomedical monitoring systems, empowering continuous measurement of critical biomarkers for monitoring of the diseased condition and health, medical diagnostics and evaluation in biological fluids like saliva, blood, and sweat. Over the past few decades, the developments have been focused on electrochemical and optical biosensors, along with advances with the non-invasive monitoring of biomarkers, bacteria and hormones, etc. Wearable devices have evolved gradually with a mix of multiplexed biosensing, microfluidic sampling and transport systems integrated with flexible materials and body attachments for improved wearability and simplicity. These wearables hold promise and are capable of a higher understanding of the correlations between analyte concentrations within the blood or non-invasive biofluids and feedback to the patient, which is significantly important in timely diagnosis, treatment, and control of medical conditions. However, cohort validation studies and performance evaluation of wearable biosensors are needed to underpin their clinical acceptance. In the present review, we discuss the importance, features, types of wearables, challenges and applications of wearable devices for biological fluids for the prevention of diseased conditions and real-time monitoring of human health. Herein, we summarize the various wearable devices that are developed for healthcare monitoring and their future potential has been discussed in detail.

Colorimetric sensors and nanoprobes for characterizing antioxidant and energetic substances

The development of analytical techniques for antioxidant compounds is important, because antioxidants that can inactivate reactive species and radicals are health-beneficial compounds, also used in the preservation of food and protection of almost every kind of organic substance from oxidation. Energetic substances include explosives, pyrotechnics, propellants and fuels, and their determination at bulk/trace levels is important for the safety and well-being of modern societies exposed to various security threats. Most of the time, in field/on site detection of these important analytes necessitates the use of colorimetric sensors and probes enabling naked-eye detection, or low-cost and easy-to-use fluorometric sensors. The use of nanosensors brings important advantages to this field of analytical chemistry due to their various physico-chemical advantages of increased surface area, surface plasmon resonance absorption of noble metal nanoparticles, and superior enzyme-mimic catalytic properties. Thus, this critical review focuses on the design strategies for colorimetric sensors and nanoprobes in characterizing antioxidant and energetic substances. In this regard, the main themes and properties in optical sensor design are defined and classified. Nanomaterial-based optical sensors/probes are discussed with respect to their mechanisms of operation, namely formation and growth of noble metal nanoparticles, their aggregation and disaggregation, displacement of active constituents by complexation or electrostatic interaction, miscellaneous mechanisms, and the choice of metallic oxide nanoparticles taking part in such formulations.

A sensing approach for automated and real-time pesticide detection in the scope of smart-farming

The increased use of pesticides across the globe has a major impact on public health. Advanced sensing methods are considered of significant importance to ensure that pesticide use on agricultural products remains within safety limits. This study presents the experimental testing of a hybrid, nanomaterial based gas-sensing array, for the detection of a commercial organophosphate pesticide, towards its integration in a holistic smart-farming tool such as the "gaiasense" system. The sensing array utilizes nanoparticles (NPs) as the conductive layer of the device while four distinctive polymeric layers (superimposed on top of the NP layer) act as the gas-sensitive layer. The sensing array is ultimately called to discern between two gas-analytes: Chloract 48 EC (a chlorpyrifos based insecticide) and Relative Humidity (R.H.) which acts as a reference analyte since is anticipated to be present in real-field conditions. The unique response patterns generated after the exposure of the sensing-array to the two gas-analytes were analysed using a common statistical analysis tool, namely Principal Component Analysis (PCA). PCA has validated the ability of the array to detect, quantify as well as to differentiate between R.H. and Chloract. The sensing array being compact, low-cost and highly sensitive (LOD in the order of ppb for chlorpyrifos) can be effectively integrated with pre-existing crop-monitoring solutions such as the gaiasense.

Recent advances in self-assemblies and sensing applications of colloidal photonic crystals

Colloidal photonic crystals (PCs), consisting of highly ordered monodisperse nanoparticles, have been carried out a great deal of research in recent decades due to the attributes of readable signal, easy modification and low cost. With these unique features, colloidal PCs have also gradually become a focus of candidates applied in sensing fields. In this review, an overview of recent advances in colloidal PCs including self-assemblies and sensing applications is illustrated. With respect to the development in self-assemblies of colloidal PCs, the review concentrates on the summary of responsive mechanisms, detection methods, responsive materials, unit cells and fabrication methods. In terms of advances in sensing application of colloidal PCs, various types of sensors are summarized based on the kinds and applications of target analytes. Furthermore, the current limitations and potential future directions of colloidal PCs in self-assemblies and sensing areas are also discussed.

Interpol review of detection and characterization of explosives and explosives residues 2016-2019

This review paper covers the forensic-relevant literature for the analysis and detection of explosives and explosives residues from 2016-2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/Resources/Documents#Publications.

Polydopamine-based molecularly imprinted thin films for electro-chemical sensing of nitro-explosives in aqueous solutions

A sensitive electrochemical sensor was developed for the detection of nitro-explosives in aqueous solutions based on thin molecularly imprinted polydopamine films. Dopamine was identified in silico, based on DFT (density functional theory) calculations with the ωB97X-D/6-31G* basis set, as the best functional monomer and electropolymerized via cyclic voltammetry (CV) in the presence of carboxylic acid-based structural analogues ('dummy' templates) for two model nitro-explosives: TNT (2,4,6-trinitrotoluene) and RDX (Research Department eXplosive, 1,3,5-trinitroperhydro-1,3,5-triazine). This approach afforded a homogenous coverage of gold electrodes with imprinted films of tunable thickness. The electropolymerized molecularly imprinted polydopamine films allowed for a 10⁵-fold sensitivity improvement over a bare gold electrode based on tracking the redox peaks of the targets by CV. This improved sensitivity is ascribed to the ability of the MIP to concentrate its target in proximity to the transduction element. The MIP films showed reproducible binding in phosphate buffer (10 mM, pH 7.4), with a dynamic range from 0.1 nM to 10 nM for both TNT and RDX and an increased selectivity over closely related structural analogues.

Recent development of biofuel cell based self-powered biosensors

BFC-based SPBs have been used as power sources for other devices and as sensors for detecting toxicity and BOM.

Molecularly Imprinted Polymer-Based Hybrid Materials for the Development of Optical Sensors

We report on the development of new optical sensors using molecularly imprinted polymers (MIPs) combined with different materials and explore the novel strategies followed in order to overcome some of the limitations found during the last decade in terms of performance. This review pretends to offer a general overview, mainly focused on the last 3 years, on how the new fabrication procedures enable the synthesis of hybrid materials enhancing not only the recognition ability of the polymer but the optical signal. Introduction describes MIPs as biomimetic recognition elements, their properties and applications, emphasizing on each step of the fabrication/recognition procedure. The state of the art is presented and the change in the publication trend between electrochemical and optical sensor devices is thoroughly discussed according to the new fabrication and micro/nano-structuring techniques paving the way for a new generation of MIP-based optical sensors. We want to offer the reader a different perspective based on the materials science in contrast to other overviews. Different substrates for anchoring MIPs are considered and distributed in different sections according to the dimensionality and the nature of the composite, highlighting the synergetic effect obtained as a result of merging both materials to achieve the final goal.

Evaluation of the solid state form of tadalafil in sub-micron thin films using nanomechanical infrared spectroscopy

Assessing physical stability of drugs is important both in the development as well as in the production phase in the pharmaceutical industry. We used nanomechanical infrared (NAM-IR) spectroscopy based on photothermal response of a nanomechanical resonator, to investigate the solid state forms of tadalafil (TAD), under various storage conditions in sub-micron thin films. The amorphous TAD was stable, when kept at normal storage conditions of 24 °C, 45% relative humidity (RH) and shielded from light, however, it crystallized after four days when it was at stress storage conditions (40 °C, 70% RH, and direct sunlight). Additionally, we found that the signals recorded with NAM-IR were comparable with the attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and that NAM-IR proved to be a suitable and time efficient method when evaluating TAD in sub 500 nm layers.

Molecularly Imprinted Polymer Materials as Selective Recognition Sorbents for Explosives: A Review

Explosives are of significant interest to homeland security departments and forensic investigations. Fast, sensitive and selective detection of these chemicals is of great concern for security purposes as well as for triage and decontamination in contaminated areas. To this end, selective sorbents with fast binding kinetics and high binding capacity, either in combination with a sensor transducer or a sampling/sample-preparation method, are required. Molecularly imprinted polymers (MIPs) show promise as cost-effective and rugged artificial selective sorbents, which have a wide variety of applications. This manuscript reviews the innovative strategies developed in 57 manuscripts (published from 2006 to 2019) to use MIP materials for explosives. To the best of our knowledge, there are currently no commercially available MIP-modified sensors or sample preparation methods for explosives in the market. We believe that this review provides information to give insight into the future prospects and potential commercialization of such materials. We warn the readers of the hazards of working with explosives.

Polymer films containing chemically anchored diazonium salts with long-term stability as colorimetric sensors

We have prepared polymeric films as easy-to-handle sensory materials for the colorimetric detection and quantification of phenol derivatives (phenols) in water. Phenols in water resources result from their presence in pesticides and fungicides, among other goods, and are harmful ecotoxins. Colorless polymeric films with pendant diazonium groups attached to the acrylic polymer structure were designed and prepared for use as sensory matrices to detect phenol-derived species in water. Upon dipping the sensory films into aqueous media, the material swells, and if phenols are present, they react with the diazonium groups of the polymer to render a highly colored azo group, giving rise to the recognition phenomenon. The color development can be visually followed for a qualitative determination of phenols. Additionally, quantitative analysis can be performed by two different techniques: a) by using a UV-vis spectrophotometer (limit of detection of 0.12 ppm for 2-phenylphenol) and/or b) by using a smartphone with subsequent RGB analysis (limit of detection of 30 ppb for 2-phenylphenol).

Bio-inspired ultrasensitive colorimetric detection of methyl isothiocyanate on nylon-6 nanofibrous membrane: A comparison of biological thiol reactivities

Living organisms, including human beings, rapidly show skin color changes after chemical poisonings, a result of toxicological or detoxification reactions caused by biological thiol compounds. On the other side, quick and portable detection of highly-volatile toxicants is an urgent need for improving human safety and personal protection, especially real-time monitoring of fumigants at low level for protection of farm workers and residents from overexposure of fumigants, vaporous pesticides. Here, we designed a rapid and portable detection method for methyl isothiocyanate (MITC) vapor by mimicking detoxification reactions of biological thiols in human bodies with MITC. The detection reaction was implemented on a nylon-6 nanofibrous membrane with ultrahigh surface areas to show color signals with the addition of Ellman's reagent. The reactivities of glutathione, N-acetyl-L-cysteine, L-homocysteine, cysteamine, and thioglycolic acid toward MITC were experimentally explored and theoretically discussed. The detection sensitivity is tunable in different biological thiol systems, which broadens the sensor applications in detection of trace amount of MITC in ambient environment and improves the protection of human safety. The new sensor system reduced the sensor operation time to 15 min and achieved the detection limit of 99 ppb, much lower than its permissible exposure limit (220 ppb).

Recent Developments in Spectroscopic Techniques for the Detection of Explosives

Trace detection of explosives has been an ongoing challenge for decades and has become one of several critical problems in defense science; public safety; and global counter-terrorism. As a result, there is a growing interest in employing a wide variety of approaches to detect trace explosive residues. Spectroscopy-based techniques play an irreplaceable role for the detection of energetic substances due to the advantages of rapid, automatic, and non-contact. The present work provides a comprehensive review of the advances made over the past few years in the fields of the applications of terahertz (THz) spectroscopy; laser-induced breakdown spectroscopy (LIBS), Raman spectroscopy; and ion mobility spectrometry (IMS) for trace explosives detection. Furthermore, the advantages and limitations of various spectroscopy-based detection techniques are summarized. Finally, the future development for the detection of explosives is discussed.

2D Photonic Crystal Hydrogel Sensor for Tear Glucose Monitoring

Photonic crystal (PC) materials have huge potentials as sensors for noninvasive and real-time monitoring glucose in tears. We developed a glucose-sensitive PC material based on monolayered colloidal crystals (MCCs). Polystyrene nanoparticles were first self-assembled into a highly ordered MCC, and this two-dimensional (2D) template was then coated by a 4-boronobenzaldehyde-functionalized poly(vinyl alcohol) hydrogel. Such a sensor efficiently diffracts visible light, whose structural color could change from red through yellow to green, as the glucose concentration altered from 0 to 20 mM, covering both tears' and bloods' physiological ranges. The sensor also represents a rapid response within 180 s at each titration of glucose, combining the characteristics of high accuracy and sensitivity in detecting the glucose concentration in tears, and this intelligent sensing material presents certain possibility for the frontier point-of-care glucose monitoring.

Stimuli Responsive Polymer-Based 3D Optical Crystals for Sensing

3D optical crystals have found their applications in sensing, actuation, optical devices, batteries, supercapacitors, etc. The 3D optical crystal devices are comprised of two main components: colloidal gels and nanoparticles. Nanoparticles self-assemble into face center cubic structures in colloidal gels. The inherent 3D optical crystal structure leads to display of structural colors on these devices following light impingement. As such, these optical properties have led to the utilization of these 3D optical crystals as self-reporting colorimetric sensors, which is the focus of this review paper. While there is extensive work done so far on these materials to exhaustively be covered in this review, we focus here in on: mechanism of color display, materials and preparation of 3D optical crystals, introduction of recent sensing examples, and combination of 3D optical crystals with molecular imprinting technology. The aim of this review is to familiarize the reader with recent developments in the area and to encourage further research in this field to overcome some of its challenges as well as to inspire creative innovations of these materials.

Nitroaromatic sensing with a new lanthanide coordination polymer [Er2(C10H4O4S2)3(H2O)6]n assembled by 2,2′-bithiophene-5,5′-dicarboxylate

A new three dimensional lanthanide-containing coordination polymer assembled from 2,2′-bithiophene-5,5′-dicarboxylic acid ([Ln₂(C₁₀H₄O₄S₂)₃(H₂O)₆]_n, Ln = Sm–Yb) was solvothermally synthesized and used as a sensor to detect nitroaromatic compounds via luminescence quenching.