Paper-based Fluorescent Sensor Research Articles

Determination of lead(II) in food samples using a functionalized paper-based fluorescent sensor modified by carbon dots.

This work discusses surface modification of cellulose paper specimens for compatibility with nitrogen and sulfur co-doped carbon dots (NSCDs) for lead ion sensing. The interaction of carbon dots (CDs) and cellulose fibers was investigated using silane or chitosan-modified cellulose papers. It was found that modified papers could reduce undesirable redistribution of CDs, during paper drying. Also, only chitosan-modified filter paper was suitable for the successful immobilization of NSCDs. The effect of paper type, chitosan amount, pH, and NSCDs concentration was also studied, and a Whatman No. 42 filter paper modified with chitosan (1% w/v), pH8.0, and an NSCD concentration of 2.5g L-1 being selected for further studies. The sensor exhibited high selectivity for lead(II) compared with other metal ions because lead(II) resulted in the most significant changes in the emitted light intensity. Variations in NSCDs fluorescence were measured using a fluorescence imaging system. The NSCDs-paper sensor showed a linear relationship between mean fluorescence intensity and lead(II) in the concentration range of 5.00-1.25 × 102 μmol L-1 with a correlation coefficient (R2 ) of 0.9988 and a detection limit of 4.50 μmol L-1 . The suggested method showed satisfying results for lead(II) determination in different samples as a fast and low-cost approach with on-site application.

Straightforward paper sensors for the detection of SSRI drugs using tyrosine functionalized GQDs: Fluorescence ‘turn-off’ turns on the crucial dosage monitoring

All socioeconomic classes are impacted by the COVID-19 epidemic, with stress being one of the biggest symptoms causing indigestion, breathlessness, heart disease, obesity, and many more. The most commonly used selective serotonin reuptake inhibitors (SSRIs) drugs include, escitalopram, sertraline, paroxetine, and fluoxetine are provided by doctors. If the medicines are not taken in the recommended dosage, at the correct intervals, which can occasionally be fatal because persons with depression are susceptible to mood fluctuations. There are no appropriate ways to monitor high dosages in clinical laboratories, the requirement for simple, novel material with cutting-edge technology to do so is essential. Herein, we report the application of a single fluorescent probe, Tyrosine-GQDs for the detection of SSRI drugs. Upon addition of SSRI drugs into the Tyrosine-GQDs, the fluorescence emission intensity of Tyrosine-GQDs decreased due to the complex formation through H-bonding which is evidenced by the rise of new peaks in fluorescence spectra and lifetime measurements. The calculated detection limit proves that the designed nanoprobe is highly sensitive and selective towards escitalopram, sertraline, paroxetine, and fluoxetine are 0.13 × 10−6 M, 0.15 × 10−6 M, 0.07 × 10−6 M, and 0.07 × 10−6 M, respectively. A paper-based fluorescent sensor is fabricated using the designed probe which is efficient in the detection of the dosage of SSRI drugs.

Facile preparation of a dual-emission paper-based fluorescent sensor based on carbon quantum dots and rhodamine B for dual-mode detection of Hg2+

In this study, carbon quantum dots (CQDs) and rhodamine B (RhB) were physically mixed to construct a highly selective and sensitive ratiometric fluorescent sensor (CQDs@RhB) for the quantitative and visual detection of Hg2+. After adding Hg2+, the emission peak of CQDs at 445 nm was quenched and the peak of RhB at 575 nm remained unchanged; the ratio of the two emission peaks had a linear relationship with the Hg2+ concentration. The CQDs@RhB had a detection range of 0–15 µM and the limit of detection (LOD) is 65.93 nM and a color change from blue to pink was visible to the naked eye under ultraviolet light. The study revealed a static quenching mechanism of CQDs@RhB. The established method was successfully applied to the detection of Hg2+ in real water and rice samples with satisfactory results. In addition, a portable fluorescent paper-based sensor platform was developed using computer software assistance. The relationship with Hg2+ concentration was constructed by converting the pictures obtained under ultraviolet light to RGB color mode for visualization and quantitative detection of Hg2+. This study provides a valuable strategy for constructing a rapid detection system for Hg2+ in the field.

A Paper-Based Fluorescent Sensor for Rapid Early Screening of Oral Squamous Cell Carcinoma

Various types of sensors play an irreplaceable role in the detection of biomarkers, but their high cost and complicated operation make it difficult to benefit ordinary people. Herein, we develop a low-cost, double-layered, paper-based fluorescent sensor (CP/HQ) structurally consisting of the upper reaction layer loaded with two oxidases (lactate oxidase and choline oxidase) and the bottom fluorescent layer that physically associates with the porphine-grafted composite fluorescent polymer colloids (PF-PDMTP/HQ). Based on the dramatic and rapid fluorescence decrease of porphine induced by the oxidation between saliva and oxidases and subsequent fluorescence resonance energy transfer from oxidized hydroquinone, the resultant fluorescent paper sensor enables us to achieve visual detection of OSCC, which was further recognized by smartphone scanning as the grayscale variation. It was found that the linear sensing range of grayscale value are 10-200 μM for lactic acid and 10-100 μM for choline, with LODs of 5.7 and 8.9 μM, respectively. More importantly, the sensor can achieve a powerful detection capability comparable to that of high-performance liquid chromatography (HPLC) in clinical settings with simple operation, demonstrating its great application potential. Our proposed sensor not only improves the accuracy of OSCC diagnosis but also provides a valuable attempt for the device modification of polymer-sensing systems and the development of non-invasive and easy-to-operate disease screening methods.

AIEE active ionic liquid based on triphenyl amine functionalized Schiff base for the selective and sensitive detection of Sn2+ ion

A triphenylamine and imidazolium based fluorescent ionic liquid (IL) [TPA-SB][Br] was synthesized and its structure was elucidated using 1H, 13C NMR, FT-IR, UV–visible spectroscopy, and mass spectrometry. Furthermore, TGA and DSC studies were carried out to establish the thermal resilience of [TPA-SB][Br]. The novel molecule revealed distinct fluorescent recognition behavior for Sn2+ ions over eleven other transition metals in the solution phase. This encouraged us to devise a paper-based fluorescent sensor embed with [TPA-SB][Br]. The paper sensor also revealed outstanding sensing properties for Sn2+ ions. As a matter of fact, aggregation induced enhanced emission (AIEE) based fluorophores are extremely pivotal in devising fluorescent sensors. Interestingly, [TPA-SB][Br] exhibited remarkable 31.2 fold increase in fluorescence intensity for 5:95 ratio of THF:water, which reveals its exceptional AIEE characteristics. Notably, ours is the first report on a paper-based Sn2+ sensor based on fluorescent ionic liquid.

A Fluorescent Molecularly Imprinted Polymer-Coated Paper Sensor for On-Site and Rapid Detection of Glyphosate

Due to the massive use and abuse of pesticides, practices which have led to serious threats to human health, the research community must develop on-site and rapid detection technology of pesticide residues to ensure food safety. Here, a paper-based fluorescent sensor, integrated with molecularly imprinted polymer (MIP) targeting glyphosate, was prepared by a surface-imprinting strategy. The MIP was synthesized by a catalyst-free imprinting polymerization technique and exhibited highly selective recognition capability for glyphosate. The MIP-coated paper sensor not only remained selective, but also displayed a limit of detection of 0.29 µmol and a linear detection range from 0.5 to 10 µmol. Moreover, the detection time only took about 5 min, which is beneficial for rapid detection of glyphosate in food samples. The detection accuracy of such paper sensor was good, with a spiked recovery rate of 92-117% in real samples. The fluorescent MIP-coated paper sensor not only has good specificity, which is helpful to reduce the food matrix interference and shorten the sample pretreatment time, but it also has the merits of high stability, low-cost and ease of operation and carrying, displaying great potential for application in the on-site and rapid detection of glyphosate for food safety.

Paper-based device for nanomolar detection of Cd2+ using AIEE-active imidazolium ionic liquid functionalized phenothiazine based Schiff-Base

A highly green fluorescent phenothiazine-based imidazolium ionic liquid (IL) [PTZ-SB][Br] was synthesized and its structure was thoroughly elucidated by 1H, 13C NMR, FT-IR, UV–visible spectroscopy and Mass spectrometry. Furthermore, thermal resilience of the IL was established by TGA and DSC investigations. The novel molecule revealed a distinct recognition for Cd2+ ions over eleven other transition metal ions. Moreover, the promising results obtained in the solution phase interested us to embed [PTZ-SB][Br] on paper strips to create a paper-based fluorescent sensor, which was examined by a portable UV light source for the on-site Cd2+ detection. Interestingly, the device demonstrated exceptional fluorescence sensing behavior towards Cd2+ with a limit of detection (LOD) of 0.16 nM. Thus, the probe has noteworthy distinct and sensitive detection ability towards Cd2+, which might find practical and on-spot applications. Noticeably, [PTZ-SB][Br] demonstrated aggregation-induced enhanced emission (AIEE) phenomenon. In fact, an incredible 38.1-fold increase in fluorescence intensity was observed for 10:90 ratio of THF:water mixture as compared that for pure THF solution of [PTZ-SB][Br]. AIEE property was further supported by DLS studies. A paper-based device for Cd2+ sensing by applying an Ionic Liquid based Schiff base is reported herein for the first time.

An irreversible paper-based profluorescent nitroxide probe for the selective detection of ascorbic acid.

Ascorbic acid (AA) or vitamin C plays multiple crucial roles, particularly as an antioxidant. This essentially biologically active molecule was selectively detected over other reductants by the synthesized profluorescent nitroxide probe ProN6via a switch-on method. After either a hydrogen atom or single electron transfer from AA to nitroxide, the resulting diamagnetic hydroxylamine was rapidly cyclized to form a fluorescent O-acylalkoxyamine. This cyclization prevented the reoxidation of the corresponding hydroxylamine to the nitroxide, leading to a high precision of detection. A kinetic fluorescence study indicated that ProN6 exhibited higher reactivity than ProN7. Density functional theory (DFT) calculations indicated that the Gibbs free energy of the AA-induced cascade reductive lactonization of ProN6 was lower than that of ProN5 and ProN7. The designed probe achieved the sensitive and specific detection of AA with detection limits of 77.9 nM and 195.9 μM in solution and on paper, respectively. The utilization of the probe as a paper-based fluorescent sensor demonstrated the good accuracy of the quantitative analysis of AA in commercial supplements.

Novel Paper-Based Fluorescent Sensor Based on N-Doped Carbon Quantum Dots (N-CQDs) and Cotton Fiber Paper (CFP) with High Selectivity and Sensitivity for the Visual Determination of Mercury (II) in Environmental Waters

A highly selective solid-state fluorescent sensor based on N-doped carbon quantum dots (N-CQDs) and cotton fiber paper (CFP) is reported for the determination of trace mercury (II)(Hg2+). The N-doped carbon quantum dots on cotton fiber paper (N-CQDs@CFP) was synthesized using a facile one-step microwave hydrothermal method. Multiple approaches were employed to fully investigate the morphology and chemical structure of the paper-based fluorescent sensor. The N-CQDs were chemically bonded onto the CFP, which offers good reproducibility and stability of the sensor. The N-CQDs@CFP showed high-intensity blue emission in dark-field imaging, and the fluorescence was quenched by Hg2+. The Hg2+ in aqueous samples was easily determined and visually monitored. There was good linearity from 0 to 250 μM, and the limit of detection was 34 nM. The paper-based fluorescent sensor provided accurate and rapid determination of Hg2+ upon comparison with flame atomic absorption spectrophotometry (FAAS). The simple preparation, rapid detection (< 5 min), low cost, and easy-handling illustrate that the reported sensor has a significant value in environmental monitoring.

Ultrasensitive Fluorogenic Probe for Detecting Ferrous Ion in Parkinson's Disease Models Using Paper-Based Fluorescent Sensor and Two-Photon Fluorescence Microscopy

Ultrasensitive Fluorogenic Probe for Detecting Ferrous Ion in Parkinson's Disease Models Using Paper-Based Fluorescent Sensor and Two-Photon Fluorescence Microscopy

Gold nanoclusters-based paper sensor for the visualized detection of nephrotoxic aristolochic acids

Aristolochic acids (AAs), the main compounds of Aristolochia plants, have aroused increasing attention due to their irreversible nephrotoxicity, carcinogenicity and mutagenicity. Common approaches for AAs monitoring usually need expensive equipment, specially trained manipulators and time-consuming procedures. Thus, it is desirable to develop a simple, fast and easy to use approach for AAs detection. Herein, we reported a fluorescent approach to detect AAs by using the lysozyme-functionalized Au nanoclusters (Lys-AuNCs) as probe. The probe shows excellent tolerance to environment temperature and pH, and it is proved to work successfully for AAs detection in real samples (serum, plasma, urine and herbal extracts). Compared with high-performance liquid chromatography method (HPLC), fluorescence method can be finished within 1 min with a recovery of 117.49 %. With the help of the visible fluorescence as signal, a paper sensor is further prepared for a direct visual monitoring of AAs. It also exhibits good stability in various conditions. After the addition of AA-I, a concentration-dependent fluorescence signal on paper was observed by naked eyes under a UV lamp. The developed paper-based fluorescent sensor provides a portable and simple method for AAs detection in herbal products and environment.

A carbon dots functionalized paper coupled with AgNPs composites platform: application as a sensor for hydrogen peroxide detection based on surface plasmon-enhanced energy transfer

A paper-based fluorescent sensor (PCD/AgNPs) consisted of CDs functionalized paper and AgNPs was developed for sensing H2O2in milk samples and cancer cells.

Novel paper- and fiber optic-based fluorescent sensor for glucose detection using aniline-functionalized graphene quantum dots

Aniline functionalized graphene quantum dots (a-GQDs) is synthesized by microwave-assisted pyrolysis of fructose. After a-GQDs are modulated using phenyl boric acid (PBA), resulting in fluorescence quenching, the a-GQDs/PBA system are employed as a fluorescent turn-on sensor for the glucose detection by the specific reaction of PBA with glucose. The prepared fluorescent sensor using a-GQDs/PBA exhibits high sensitivity and selectivity toward glucose. In addition, the paper-based fluorescent sensor is prepared for portable sensing devices by printing the a-GQDs ink with a commercial inkjet printer, demonstrating a superior visual glucose detection and a good sensitive performance for the detection of glucose in a blood serum and tear samples. Furthermore, the a-GQDs/hydrogel film is evaluated for a wearable sensor as well as fiber optic-based sensor for highly sensitive and fast on-site glucose detection. The prepared fiber optic sensor exhibits remarkable glucose sensing performance with a fast response, a low detection limit of 2.1 μM and excellent recyclability. Finally, the a-GQD/PBA system exhibits excellent biocompatibility and was applied to detect glucose in HeLa cells with satisfactory results. These results provide a novel approach for developing low-cost and flexible sensors for the portable and visual detection of glucose with high sensitivity and selectivity.

Smart-phone, paper-based fluorescent sensor for ultra-low inorganic phosphate detection in environmental samples

A major goal of environmental agencies today is to conduct point-of-collection monitoring of excess inorganic phosphate (Pi) in environmental water samples for tracking aquatic “dead zones” caused by algae blooms. However, there are no existing commercial devices which have been miniaturized and are suitable for the point-of-need-testing (“PONT”) that is required to fully map a large region, such as the Florida Everglades. To solve this challenge, a reflection-mode fluorescence-sensing apparatus was developed, leveraging an environmentally sensitive fluorophore (MDCC) bound to a bacterial phosphate-binding protein to generate a fluorescent optical signal proportional to the concentration of (Pi) present. The combined end-to-end integrated sensor system had a response time of only 4 s, with minimal effects of common interfering agents and a linear range spanning from 1.1 to 64 ppb. To support ease-of-use during PONT, the platform incorporated disposable wax-printed paper strip sample pads and a smartphone camera detection system. Since the EPA threshold is currently 30 ppb to prevent eutrophication, this system serves as a rapid test of whether a region is compliant.

Fast and selective detection of mercury ions in environmental water by paper-based fluorescent sensor using boronic acid functionalized MoS2 quantum dots

In this study, the B-MoS2 QDs, boronic acid functionalized MoS2 quantum dots, are synthesized by a simple aminoacylation reaction between MoS2 QDs and 3-aminobenzeneboronic acid (APBA). It not only exhibits excellent thermo-stability, photo-stability and good salt tolerance, but shows excellent fluorescence stability even under industrial wastewater with high concentration. These good characters can be used to construct a new fluorescence sensor for sensitive and selective detection of mercury ions (Hg2+). The fluorescence intensity of B-MoS2 QDs linearly decreases with the increase of Hg2+ concentration ranging from 0.005 to 41 μmol L−1, and the limit of detection as low as 1.8 nmol L−1. Due to the mercury ion-promoted transmetalation reaction of aryl boronic acid, this proposed method exhibits fast response, ultra-sensitivity and high selectivity for analysis of Hg2+ in different environmental water, and which also uses to online monitoring of Hg2+. The B-MoS2 QDs–based test paper can be used to detect the trace amounts of Hg2+ under UV lamp by naked eyes, suggesting that the proposed method has potential application in on-site monitoring of environmental Hg2+.

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.

Multipurpose sensing applications of biocompatible radish-derived carbon dots as Cu2+ and acetic acid vapor sensors.

A recent trend in the preparation of carbon dots, optically unique nanomaterials, revolves around the use of readily-available, low-cost natural resources as precursors and their multipurpose applications. In this work, a hydrothermal method for preparing biocompatible carbon dots from radish was developed. The carbon dots were then tested for sensing of Cu2+ and acetic acid vapor. The carbon dots exhibited blue emission under UV illumination with, a quantum yield of 15%. The fluorescence emission was selectively quenched when Cu2+ ions were added, giving a detection limit of 0.16 μM. A paper-based fluorescent sensor was fabricated and shown to sense Cu2+ with a limit of detection of 6.8 μM. The carbon dots were able to determine the Cu2+ concentration in real water samples, with excellent recovery and reliability. The carbon dots were also used as the sensing material in an optical electronic nose, and tested for real-time detection of acetic acid vapor. Using principal component analysis, different ratios of acetic acid to methanol in solution were successfully identified with a detection limit of 15.5%. The acetic acid concentration in a real vinegar sample was also accurately determined. Our results demonstrated that label-free carbon dots derived from readily available radish can be simply used as versatile probes, giving them potential uses in multipurpose sensing applications.

Dual-mode fluorescence biosensor platform based on T-shaped duplex structure for detection of microRNA and folate receptor

In this work, a microfluidic paper-based fluorescent sensor device was constructed for quantitative detection of microRNA (miRNA) and determination of the expression of folate receptor (FR) on the cell surface. It is worth pointing out that simultaneous detection of two biomarkers in cancer was achieved through dynamic self-assembly of T-shaped duplex structure. T-shaped duplex structure can respond to specific triggers and convert to an output due to the conformation changes, it is meaningful to fabricate T-shaped duplex structure into powerful biosensors that can monitor chemical stimuli. Moreover, lamellar MnO2 nanosheets were synthesized, which exhibited excellent quenching ability via adsorbed fluorophore-labeled ssDNA, but the adsorption of the dsDNA was significantly lower than ssDNA because of the shielding of nucleobase pairs by the phosphate groups. This newly designed biosensor provided a sensitive detection of miR-21 from 0.01 to 5.0 fM with a relatively low detection limit of 0.0033 fM. Besides, the present sensing system has a detection of FR in the range from 2.0 to 30.0 ng/mL with the detection limit of 0.667 ng/mL. As biological markers for disease diagnosis, the detection of FR and miRNA will provide a new approach and therapeutic tool for early clinical diagnosis.

Paper-based fluorescent sensor via aggregation induced emission fluorogen for facile and sensitive visual detection of hydrogen peroxide and glucose

Hydrogen peroxide (H2O2), an important reactive oxygen species (ROS), is related to the oxidative stress in organisms, and plays important roles in a variety of cellular activities as well. So it is of crucial importance to develop sensitive and accurate sensing strategies to detect H2O2 in biological systems. Herein, by taking advantage of the unique emission characteristics of aggregation induced emission (AIE) fluorogens, we proposed a non-enzymatic fluorescence platform for facile and sensitive detection of H2O2, both in solution state using fluorescence spectrometer and on paper-based sensor via visual inspection. Through the reaction between L-cysteine and H2O2, the fluorescence of TPE-M-L, an AIE fluorogen formed between maleimide-functionalized tetraphenylethene (TPE-M) and L-cysteine, is quenched, and highly sensitive non-enzymatic H2O2 assay is readily carried out. The limit of detection (LOD) of 10nM in solution state and 2.5μM on paper-based sensor were obtained for H2O2 detection, which were superior or comparable to those previously reported in literature. Moreover, by integrating glucose oxidase with the AIE fluorogen of TPE-M-L, highly sensitive and selective glucose detection was also conveniently achieved both in solution state and on paper-based sensor by the as-proposed strategy, with the LODs of 50nM in solution state and 10μM via visual observation, much better than those obtained by other fluorescence methods. The as-proposed sensing strategy was also successfully applied to assay glucose in human serum samples. Therefore, the paper-based fluorescence sensor exhibits the advantages of simple fabrication, high sensitivity and portability, and has great potential to be applied in on-site assay of H2O2 and glucose in real samples.

Paper-based fluorescent sensor for rapid naked-eye detection of acetylcholinesterase activity and organophosphorus pesticides with high sensitivity and selectivity

Various strategies have been proposed for the sensing of acetylcholinesterase (AChE) activity and organophosphorus pesticides (OPs). However, the practical application of most methods is restricted by their intrinsic drawbacks such as complexity, long analysis time, and high cost. Thus, it is highly desirable to develop simple, fast and sensitive approaches for AChE activity and OPs detection. Herein, we reported a simple paper-based fluorescent sensor (PFS) based on the aggregation induced emission (AIE) effect of tetraphenylethylene (TPE) and the addition reaction capability of maleimide, which has been used as a powerful tool for rapid naked-eye detection of AChE activity and OPs. The introduction of TPE provides the probe with unique fluorescence property in solid state and is of great importance for improving the sensitivity of PFS. The hydrolysis product of acetylthiocholine catalyzed by AChE induced the maleimide ring destruction and activated the fluorescence performance of TPE. Given that AChE activity can be specifically inhibited by OPs, the as-proposed PFS can also be utilized for sensitive detection of OPs. Meanwhile, the variation of fluorescence signal can be readily detected by naked eyes, and low detection limits of 2.5mUmL−1 and 0.5ngmL−1 for AChE activity and OPs are obtained, respectively. Moreover, it has been successfully applied for AChE activity and OPs detection in diluted human serum samples, showing its great potential to be applied in real samples. Thus, this strategy possesses considerable advantages of simplicity, rapid detection, portability, cost efficiency and visualization.