Cellulose-based fluorescent sensor for visual and versatile detection of amines and anions

Recent Advances in Thiourea Based Colorimetric and Fluorescent Chemosensors for Detection of Anions and Neutral Analytes: A Review

Thioureas and their derivatives are organosulfur compounds having excellent biological and non-biological applications. These compounds contain S- and N-, which are nucleophilic and allow for establishing inter-and intramolecular hydrogen bonding. These characteristics make thiourea moiety a very important chemosensor to detect various environmental pollutants. This article covers a broad range of thioureas and their derivatives that are used for highly sensitive, selective, and simple fluorimetric (turn-off and turn-on), and colorimetric chemosensors for the detection and determination of different types of anions, such as CN-, AcO-, F-, ClO- and citrate ions, etc., and neutral analytes such as ATP, DCP, and Amlodipine, etc., in biological, environmental, and agriculture samples. Further, the sensing performances of thioureas-based chemosensors have been compared and discussed, which could help the readers for the future design of organic fluorescent and colorimetric sensors to detect anions and neutral analytes. We hope this study will support the new thoughts to design highly efficient, selective, and sensitive chemosensors to detect different analytes in biological, environmental, and agricultural samples.

A colorimetric and NIR fluorescent probe for ultrafast detecting bisulfite and organic amines and its applications in food, imaging, and monitoring fish freshness

Herein, for the first time, we have successfully constructed a novel near-infrared (NIR) emission fluorescent probe Dpyt for ultrafast detecting (within 5 s) bisulfate and organic amines based on a 1,2-dihydrocyclopenta[b]chromene-barbiturate conjugation system. Upon addition of bisulfate or organic amines, Dpyt displayed a distinct color change from blue to colorless or from purple to blue, respectively, suggesting that the Dpyt can be used to detect two analytes by the naked eye. Based on quantum chemistry calculations, the fluorescence quenching of Dpyt after the addition of HSO3- is caused by the photoinduced electron transfer (PET) process of the adduct Dpyt-HSO3-. The fluorescence enhancement of Dpyt caused by most organic amines is due to the enhanced intramolecular charge transfer (ICT) process of deprotonated Dpyt. Notably, Dpyt can be applied for detecting HSO3- in actual food samples such as red wine and sugar, as well as for imaging of HSO3- and representative propylamine in living cells. And more importantly, indicator labels constructed by filter paper loaded with Dpyt can visually monitor the freshness of salmon in real-time by daylight and fluorescence dual-mode. The comparison with national standard method of China manifests that indicator labels are a valid tool to assess the freshness of seafood.

Recent studies on proteins and polysaccharides-based pH-responsive fluorescent materials

Polymer-based pH-responsive fluorescent materials have the characteristics of fast response, real-time monitoring, visualisation, and easy forming. Consequently, they have attracted widespread attention in wound healing, sweat monitoring, security and anti-counterfeiting, freshness detection of aquatic products, metal-ion sensing and bioimaging. This paper analyses the preparation principles and characteristics of pH-responsive fluorescent materials based on cellulose, chitosan and proteins. It then outlines the fluorescence properties, environmental response mechanisms and applications of various luminescent materials. Next, the research indicates that amines, N-heterocyclic rings, carboxyl groups and amino plasmonic groups on the fluorescent molecule structure and polymer skeleton appear to change the degree of ionisation under acid or alkali stimulation, which affects the light absorption ability of chromophore electrons, thus producing fluorescence changes in fluorescent materials under different pH stimuli. On this basis, the challenges and growth encountered in the development of proteins and polysaccharides-based pH-responsive fluorescent materials were prospected to provide theoretical references and technical support for constructing pH-responsive fluorescent materials with high stability, high sensitivity, long-lasting pH-response and wide detection range.

Recent developments in lignin-based fluorescent materials

Biomass-based fluorescent materials are an alternative to plastic-based materials for their multifunctional applications. Lignin, an inexpensive and easily available raw material, demonstrates outstanding environment-responsive properties such as pH, metal ions, dyes sensing, bioimaging and so on. To date, only a little work has been reported on the synthesis of lignin-based fluorescent materials. In this review report, synthetic approaches and light-responsive applications of lignin-based fluorescent carbon dots and other materials are summarized. The results reveal that lignin-based fluorescent carbon dots are prepared by hydrothermal method, exhibit small size <10 nm, reveal significant quantum yield, biocompatibility, non-toxicity, photostability and display substantial tunable emission and can be efficiently employed for sensing, bioimaging and energy storage applications. Finally, the forthcoming challenges, investigations, and options open for the chemical and/or physical modification of lignin into fluorescent materials for future applications are well-addressed. To our knowledge, this is the first comprehensive review report on lignin-based fluorescent materials and their light-responsive applications. In addition, this review will attract remarkable consideration and thrust for the researchers and biochemical technologists working with the preparation of lignin-based fluorescent materials for broad applications.

In Situ Optical Detection of Amines at a Parts-per-Quadrillion Level by Severing the Through-Space Conjugated Supramolecular Domino

Conventional fluorophores suffer from low sensitivity and selectivity in amine detection due to the inherent limitations in their "one-to-one" stoichiometric sensing mechanism. Herein, we propose a "one-to-many" chain reaction-like sensing mechanism by creating a domino chain consisting of one fluorescent molecule (e.g., PTF1) and up to 40 nonemissive polymer chains (pPFPA) comprising over thousand repeating units (PFPA). PTF1 (the domino trigger) interacts with adjacent PFPA units (the following blocks) through polar-π interactions and initiates the domino effect, creating effective through-space conjugation along pPFPA chains and generating amplified yellow fluorescent signals through charge transfer between PTF1 and pPFPA. Amine exposure causes rapid dismantling of the fluorophore-pPFPA-based domino chain and significantly reduces the amplified emissions, thus providing an ultrasensitive method for detecting amines. Relying on the above merits, we achieve a limit of detection of 177 ppq (or 1.67 × 10-12 M) for triethylamine, which is nearly 4 orders lower than that of previous methods. Additionally, the distinct reactivity of pPFPA toward different amines allows for the discrimination of primary, secondary, and tertiary amines. This study presents a "domino effect" sensing mechanism that has not yet been reported and provides a general approach for chemical detection that is beyond the reach of conventional methods.

Boron Adsorption Kinetics of Microcrystalline Cellulose and Polymer Resin

Tailoring boron-polysaccharide interactions is an important strategy for developing functional soft materials such as hydrogels, fire retardants, and sorbents for environmental remediation, for example, using lignocellulosic biomass. For such applications to be realized, it is paramount to understand the adsorption kinetics of borate anions on cellulose and their local structures. Here, the kinetic aspects of boron adsorption by microcrystalline cellulose, lignin, and polymeric resin are investigated and compared. Borate anions interact with the vicinal diols in the glucopyranoside moieties of cellulose to yield chemisorbed boron chelate complexes. In contrast to cellulose, technical lignin contains fewer cis-vicinal diols, and it does not have a tendency to form such chelate complexes upon treatment with the aqueous boric acid solution. The formation kinetics and stability of these chelate complexes strongly depend on nanoscale structures, as well as reaction conditions such as pH and concentration of the sorbate and sorbent. Specifically, insights into the distinct boron adsorption sites were obtained by solid-state one-dimensional (1D) ¹¹B magic-angle spinning NMR and the local structures and intermolecular interactions in the vicinities of boron chelate complexes are elucidated by analyzing two-dimensional (2D) ¹H-¹³C and ¹¹B-¹H heteronuclear correlation NMR spectra. The total boron adsorption capacity of cellulose is estimated to be in the 1.3-3.0 mg range per gram of sorbent, which is lower than the boron adsorption capacity of a polystyrene-based resin, ∼17.2 mg of boron per gram of Amberlite IRA 743. Our study demonstrates that the local backbone and side chain flexibility as well as the structures of polyol groups play a significant role in determining the kinetic and thermodynamic stability of chelate complexes, yielding to different boron adsorption capabilities of lignocellulosic polymers.

A Robust Ratiometric Fluorescent Sensor Based on Covalent Assembly of Dipeptides and Biomolecules for the High-Sensitive and Optosmart Detection of Pyrethroids

In this study, two ultrashort dipeptides, diphenylalanine (FF) or C-terminal amidated diphenylalanine (DPA), were covalently self-assembled with genipin to obtain two well-defined supramolecular peptide nanoparticles for the detection of pyrethroids. DPA-genipin nanoparticles (PNPs) demonstrated excellent dual-emission fluorescence characteristics, tunable particle size, and robust photostability. Parallel to this, PNPs showed a ratiometric fluorescence response to λ-cyhalothrin (LC) with a distinct green-to-red color transition. The satisfactory self-calibration capability of the ratiometric system enabled PNPs to respond sensitively to LC in a wide range (5-800 μg/L) with a lower limit of detection of 0.034 μg/L. The introduction of a smartphone application made it easy to develop an intelligent evaluation platform based on PNPs, which had been proven to be applicable for on-site visualization of LC in agricultural products. The platform proposed here may be a new application of peptide self-assembly in sensing, with both important food safety implications and great economic value.

A Portable Smartphone-Based System for the Detection of Blood Calcium Using Ratiometric Fluorescent Probes

Hypocalcemia is a disease that adversely affects the production and reproduction of dairy cows. A portable device for rapid bovine blood calcium sensing has been growing in demand. Herein, we report a smartphone-based ratiometric fluorescence probe (SRFP) platform as a new way to detect and quantify calcium ions (Ca²⁺) in blood serum. Specifically, we employed a cost-effective and portable smartphone-based platform coupled with customized software that evaluates the response of Ca²⁺ ions to ratiometric fluorescence probe in bovine serum. The platform consists of a three-dimensional (3D) printed housing and low-cost optical components that excite fluorescent probe and selectively transmit fluorescence emissions to smartphones. The customized software is equipped with a calibration model to quantify the acquired fluorescence images and quantify the concentration of Ca²⁺ ions. The ratio of the green channel to the red channel bears a highly reproducible relationship with Ca²⁺ ions concentration from 10 μM to 40 μM in bovine serum. Our detection system has a limit of detection (LOD) of 1.8 μM in bovine serum samples and the recoveries of real samples ranged from 92.8% to 110.1%, with relative standard deviation (RSD) ranging from 1.72% to 4.89%. The low-cost SRFP platform has the potential to enable campesino to rapidly detect Ca²⁺ ions content in bovine serum on-demand in any environmental setting.

A fully water-soluble Calix[4]arene probe for fluorometric and colorimetric detection of toxic hydrosulfide and cyanide ions: Practicability in living cells and food samples

Although hydrosulfide and cyanide anions play important roles in daily life that they are available in a lot of foods. However, their excess amounts contaminate water, land, and food and cause serious problems to human health. Herein, we introduce a water-soluble macrocyclic sensor based-on Calix[4]arene (MPI-Calix[4]) with dual response sites for fluorescence recognizing cyanide (CN^-) and hydrogen sulfide (HS^-) under longwave light. MPI-Calix[4] exhibits a high selectivity and sensitivity in the detection of CN^- and HS^-, where the limits of detection were as low as 0.115 and 8.12 μmol/L, respectively. The cell imaging studies shows that this probe can be easily used in the detection of CN^- and HS^- on living cells. Full understanding of these results paved a fruitful system to improve an applicable analytical process for food safety and quality.

Dual modification of cellulose with esterification and carbonation in DMSO/DBU/CO2 system as fluorescent additive for pH detection

An easy and effective way to synthesize dual-functionalized cellulose derivatives with processability and fluorescence functionality by one-pot modification of successive esterification and carbonation under mild condition is established with the use of DMSO/DBU/CO₂ system. Accordingly, four kinds of dual-functionalized cellulose derivatives with rather good fluorescent response are obtained. After blending the synthesized dual-functionalized cellulose derivative with cellulose acetate as functional additive in solution, cast film with the elastic modulus, stress and strain reaches to 2.2 GPa, 34.1 MPa and 5.7% is prepared. Besides, the cast film also exhibits the ability to detect the pH value at 12-14 with detection accuracy of 0.4 through the change of fluorescent color. This research shows a simple but effective way to prepare dual-functionalized cellulose derivatives for the high-quality applications in field of detection.

Double-site-based a smart fluorescent sensor for logical detecting of sulphides and its imaging evaluation of living organisms

Thiophenol and hydrosulphite are a group of toxic environmental pollutants, which contaminate land, water and food exhibiting a serious risk to human health. Herein, we reported a xanthene dye-based sensor (DSF) with dual well-known response sites for visual detecting PhSH and HSO₃^-. Specifically, when DSF reacted with PhSH firstly, the color of the solution changed to blue with bright red fluorescence emission. After added with HSO₃^-, the color of the solution became yellow, and emitted yellow fluorescence signal. However, DSF was first added with HSO₃^-, the color of the solution changed to purple with no-fluorescence emission, and then PhSH was added, the color of the solution changed to yellow with a bright yellow fluorescence. Notably, DSF exhibited high sensitivity and selectivity for PhSH and HSO₃^- detection with a very low detection limits of 2.27 nM and 22.91 nM, respectively. More importantly, DSF could detect PhSH and HSO₃^- in water, real-food and biological systems. Therefore, the experimental results showed DSF as a robust new logical monitoring tool for the detection of PhSH and HSO₃^- in water, real-food samples and biological systems.

Aromatic fluorine atom-induced highly amine-sensitive trimethine cyanine dye showing colorimetric and ratiometric fluorescence change

The prepared ring-perfluorinated trimethine cyanine dye 2a has a significantly higher response to n-hexylamine than the non-fluorinated dye 2b, and exhibited a dual change in the solution and on filter paper and fluorescence color at widely shifted wavelengths, visible to the naked eye.

Recent studies on cellulose-based fluorescent smart materials and their applications: A comprehensive review

The progress of bio-based fluorescent smart materials and their multifunctional applications have attained increasing interest in the recent decades. Cellulose is among the cheapest and widespread raw material on earth which can be modified into diverse useful materials. This review summarizes the chemical modification of cellulose into smart fluorescent materials. This further highlights on the fabrication of the prepared fluorescent materials into films, fibers, paper strips, carbon dots, hydrogels and solutions which are applied for the sensing of toxic metals and anions, pH, bioimaging, common organic solvents, aliphatic and aromatic amines, nitroaromatics, fluorescent printing, coating, and anti-counterfeiting applications. Finally, the discussion about the upcoming investigations, challenges, and options open for the cellulose-based luminescence sensors are communicated. We believe that this review will appeal more and more attention and curiosity for the chemists, biochemists, and chemical engineers working with the synthesis of cellulose-based fluorescent materials for widespread applications.

A Review on the Role and Performance of Cellulose Nanomaterials in Sensors

Sensors and biosensors play a key role as an analytical tool for the rapid, reliable, and early diagnosis of human diseases. Such devices can also be employed for monitoring environmental pollutants in air and water in an expedited way. More recently, nanomaterials have been proposed as an alternative in sensor fabrication to achieve gains in performance in terms of sensitivity, selectivity, and portability. In this direction, the use of cellulose nanomaterials (CNM), such as cellulose nanofibrils (CNF), cellulose nanocrystals (CNC), and bacterial cellulose (BC), has experienced rapid growth in the fabrication of varied types of sensors. The advantageous properties are related to the supramolecular structures that form the distinct CNM, their biocompatibility, and highly reactive functional groups that enable surface functionalization. The CNM can be applied as hydrogels and xerogels, thin films, nanopapers and other structures interesting for sensor design. Besides, CNM can be combined with other materials (e.g., nanoparticles, enzymes, carbon nanomaterials, etc.) and varied substrates to advanced sensors and biosensors fabrication. This review explores recent advances on CNM and composites applied in the fabrication of optical, electrical, electrochemical, and piezoelectric sensors for detecting analytes ranging from environmental pollutants to human physiological parameters. Emphasis is given to how cellulose nanomaterials can contribute to enhance the performance of varied sensors as well as expand novel sensing applications, which could not be easily achieved using standard materials. Finally, challenges and future trends on the use of cellulose-based materials in sensors and biosensors are also discussed.

Nanobioengineered Sensing Technologies Based on Cellulose Matrices for Detection of Small Molecules, Macromolecules, and Cells

Recent advancement has been accomplished in the field of biosensors through the modification of cellulose as a nano-engineered matrix material. To date, various techniques have been reported to develop cellulose-based matrices for fabricating different types of biosensors. Trends of involving cellulosic materials in paper-based multiplexing devices and microfluidic analytical technologies have increased because of their disposable, portable, biodegradable properties and cost-effectiveness. Cellulose also has potential in the development of cytosensors because of its various unique properties including biocompatibility. Such cellulose-based sensing devices are also being commercialized for various biomedical diagnostics in recent years and have also been considered as a method of choice in clinical laboratories and personalized diagnosis. In this paper, we have discussed the engineering aspects of cellulose-based sensors that have been reported where such matrices have been used to develop various analytical modules for the detection of small molecules, metal ions, macromolecules, and cells present in a diverse range of samples. Additionally, the developed cellulose-based biosensors and related analytical devices have been comprehensively described in tables with details of the sensing molecule, readout system, sensor configuration, response time, real sample, and their analytical performances.

Predicting Dimensions in Microfluidic Paper Based Analytical Devices

The main problem for the expansion of the use of microfluidic paper-based analytical devices and, thus, their mass production is their inherent lack of fluid flow control due to its uncontrolled fabrication protocols. To address this issue, the first step is the generation of uniform and reliable microfluidic channels. The most common paper microfluidic fabrication method is wax printing, which consists of two parts, printing and heating, where heating is a critical step for the fabrication of reproducible device dimensions. In order to bring paper-based devices to success, it is essential to optimize the fabrication process in order to always get a reproducible device. Therefore, the optimization of the heating process and the analysis of the parameters that could affect the final dimensions of the device, such as its shape, the width of the wax barrier and the internal area of the device, were performed. Moreover, we present a method to predict reproducible devices with controlled working areas in a simple manner.

Synthesis and Fluorescent Thermoresponsive Properties of Tetraphenylethylene-Labeled Methylcellulose

Functional polymer, especially the one based on renewable and sustainable materials, has attracted increasing attention to satisfy the growing demand for the design of stimuli-responsive devices. Methylcellulose (MC) is a water-soluble derivative of cellulose, which has been widely used in many fields for its biocompatibility and biological inertness. In this work, MC is labeled by tetraphenylethylene (TPE) via azide-alkyne click reaction to obtain a fluorescent cellulose-based derivative of MC-TPE. The degree of substitution of MC-TPE is determined to be 0.074, which can be self-assembled into micelles in water with the size of 42 ± 6 nm. MC-TPE shows thermoresponsivity and thermoreversibility in size, transmittance, and fluorescence, enabling it to work as a fluorescent thermosensor. Moreover, MC-TPE exhibits nontoxicity and biocompatibility, allowing its application in MCF-7 cell imaging. Therefore, this newly functional natural polymer shows promising potentials in the fields of sensing and bioimaging.

Colorimetric Differentiation of Multiple Oxidizing Anions Based on Two Core-Shell Au@Ag Nanoparticles with Different Morphologies as Array Recognition Elements

The efficient discrimination of oxidizing anions is of considerable importance in environmental monitoring. Here, for the first time, we have developed a simple and fast colorimetric sensor array for detection and identification of oxidizing anions, which takes advantage of the etching of the Ag shell of two core-shell Au@Ag nanoparticles (Au@Ag nanospheres (Au@Ag NPs) and Au@Ag nanocubes (Au@Ag NCs)) by oxidizing anions. The differential etching ability of various oxidizing anions to the Ag shell of the two Au@Ag nanoparticles resulted in different absorbance and color change of the nanoparticles. Thus, employing Au@Ag NPs and Au@Ag NCs as the array's receptors and the indicators, six oxidizing anions (i.e., BrO₃^-, Cr₂O₇^2-, ClO₄^-, IO₃^-, IO₄^-, and MnO₄^-) down to 10 nM could be identified from each other by their own colorimetric response patterns. Moreover, the complex mixtures of oxidizing anions could be well discriminated. Most importantly, the sensor array was successfully applied to the discrimination of oxidizing anions in river water and tap water samples.