Portable Fluorescent Sensor Research Articles

Self-assembly monolayer fluorescent probe on alumina substrate enabling highly sensitive detection of arsenite ions in groundwater

The contamination of arsenic in groundwater is an urgent issue that demands immediate attention. The presence of arsenic in water exceeding the acceptable threshold of 10 ppb poses a significant threat to both the environment and human health. Therefore, it is essential to develop highly sensitive detection techniques for accurately assessing arsenic contamination levels in groundwater. In this study, a fluorescent sensitive membrane (Al2O3-AHM) was fabricated by growing a turn-on fluorescent probe (AHM) on alumina substrate via self-assembled monolayer (SAM) strategy for the ultrasensitive detection of arsenite ions (AsO33-). When integrated into portable laser-induced fluorescence sensors (LIFs), the Al2O3-AHM enables highly sensitive detection of AsO33- with an impressively low detection limit of 4.65 ppb. Furthermore, this portable fluorescence sensor platform has been successfully utilized for detecting the concentration of AsO33- in real groundwater samples. The results obtained from this method are generally consistent with those from Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) analysis, demonstrating its reliability and accuracy. Overall, this study presents a new design concept and method for future development of membrane-based fluorescent sensors for real-time and on-site detection of heavy metal ions.

A sensitive lateral flow test strip sensor for visual detection of acid red 18 in food using bicentric-emission carbon dots.

Hazardous synthetic colorants have found widespread use in food production, and excessive consumption of these pigments can pose potential risks to human health. In this study, we propose an ultrasensitive fluorescence method for the analysis of Acid Red 18 (AR18) in food products. The method is based on the nitrogen-doped carbon dots (N-CDs) derived from tris and resorcinol through a hydrothermal way. The as-synthesized N-CDs exhibit two emission centers at 425 nm and 541 nm, corresponding to the excitation wavelengths of 377 nm and 465 nm, respectively. Upon the addition of AR18, the fluorescence intensity at 541 nm significantly decreases with a simultaneous, though less pronounced, reduction in the intensity at 425 nm, which is attributed to the localization of fluorescence resonance energy transfer (L-FRET). Specifically, a novel ratiometric fluorescent probe was constructed based on the extracted data from the 3D fluorescence excitation-emission matrix. This probe demonstrates a wide linear range from 0.0539 to 30 μM and a low limit of detection (LOD) of 53.9 nM. For practical applications, a portable fluorescent sensor based on a lateral flow test strip (LFTS) was designed for real-time monitoring of AR18. Color channel values were determined using a smartphone application, resulting in a satisfactory LOD of 75.3 nM. Furthermore, the suitability of the proposed ratiometric fluorescent probe was validated through the detection of AR18 in real food samples, consistently achieving recovery rates in the range of 99.7-101.4%. This research not only expands the scope of CDs in sensing fields, but also provides an effective strategy for the development of an excellent platform for real-time AR18 detection, contributing to public food safety.

Engineering of polarity-responsive fluorescent probe for real-time measurement and visualization of total polar materials in edible oils

The content of total polar materials (TPM) in edible oils is generally accepted as a reliable indicator of the quality of edible oils. A high TPM value may signify that the flavor has been compromised and its consumption may lead to adverse effects on human health. However, the lack of convenient and user-friendly detection methods for the detection of TPM remains a challenge. To address this, a sensitive polarity-responsive fluorescent probe has been designed. A good linear relationship was observed for the ratio of the intensity of green to red fluorescence signal (I504 nm/I625 nm) and the TPM content over the range 1.1–29.3% for soybean oil and 0.1–27.5% for salad oil, respectively. A portable fluorescence sensor system was constructed, which provided a stable platform for the convenient detection of TPM via naked eye observation. These results indicate that the probe has great potential for TPM detection of edible oils in the food safety industry.

Luminescent Guests Encapsulated in Metal–Organic Frameworks for Portable Fluorescence Sensor and Visual Detection Applications: A Review

Metal-organic frameworks (MOFs) have excellent applicability in several fields and have significant structural advantages, due to their open pore structure, high porosity, large specific surface area, and easily modifiable and functionalized porous surface. In addition, a variety of luminescent guest (LG) species can be encapsulated in the pores of MOFs, giving MOFs a broader luminescent capability. The applications of a variety of LG@MOF sensors, constructed by doping MOFs with LGs such as lanthanide ions, carbon quantum dots, luminescent complexes, organic dyes, and metal nanoclusters, for fluorescence detection of various target analyses such as ions, biomarkers, pesticides, and preservatives are systematically introduced in this review. The development of these sensors for portable visual fluorescence sensing applications is then covered. Finally, the challenges that these sectors currently face, as well as the potential for future growth, are briefly discussed.

Extraction of physicochemical properties from the fluorescence spectrum with 1D convolutional neural networks: Application to olive oil

One of the main challenges for olive oil producers is the ability to assess oil quality regularly during the production cycle. The quality of olive oil is evaluated through a series of parameters that can be determined, up to now, only through multiple chemical analysis techniques. This requires samples to be sent to approved laboratories, making the quality control an expensive, time-consuming process, that cannot be performed regularly and cannot guarantee the quality of oil up to the point it reaches the consumer. This work presents a new approach that is fast and based on low-cost instrumentation, and which can be easily performed in the field. The proposed method is based on fluorescence spectroscopy and one-dimensional convolutional neural networks and allows to predict five chemical quality indicators of olive oil (acidity, peroxide value, UV spectroscopic parameters K 270 and K 232 , and ethyl esters) from one single fluorescence spectrum obtained with a very fast measurement from a low-cost portable fluorescence sensor. The results indicate that the proposed approach gives exceptional results for quality determination through the extraction of the relevant physicochemical parameters. This would make the continuous quality control of olive oil during and after the entire production cycle a reality. • We present the application of 1D-CNN to single fluorescence spectra without pre- and post- processing of the data. • We discuss a method for the application of 1D-CNN to small datasets. • The 1D-CNN determines the physicochemical parameters within the instrument errors. • The proposed solution has the potential to substitute chemical analyses to assess the quality of olive oil.

A Portable Fluorescence Sensor with Improved Performance for Aniline Monitoring

AbstractAniline is an important biomarker in human exhaled breath for lung cancer, thus aniline sensing is of paramount importance. However, highly sensitive and selective detection of aniline in high moisture environment of exhaled breath is still challenging. In this work, a new fluorescence sensor for aniline with ultrahigh sensitivity is constructed. The o‐carborane modified pyromellitic diimide derivative (CB‐PMI) is designed and prepared as the sensitive layer for the fluorescence sensor. As‐prepared sensing films exhibit a highly improved response toward aniline vapor. The good sensing performance of the fluorescence films in terms of response speed, selectivity, and reusability is also realized, and the detection limit can be as low as 0.1 ppt. The detection linear slope ranges from 1 to 50 ppt. In addition, a homemade portable sensing platform is successfully constructed, which may be a promising prototype for the future detection of modulating breath samples. The reported fluorescence sensor offers a new paradigm for the simple, low cost, and noninvasive diagnosis of lung cancer.

Construction of integrated and portable fluorescence sensor and the application for visual detection in situ

The development of portable and low-cost fluorescence sensors is significant for on-site detection. Herein, a novel fluorescence sensor integrating power source, light source, filter, sample cell and smartphone was constructed. The model of fluorescence sensor was designed by using Autodesk Computer Aided Design (CAD) software, and printed with 3D printing technology, followed by assembling with various components. With advantages of convenient carrying, good stability, wide applicability and low cost, the fluorescence sensor showed great adaptability for on-site visual detection. Nitrite was chosen as the model of analyte, and ratiometric fluorescent probe (B/R-CDs) was employed as the identification and signal element for detecting nitrite. With the increase of nitrite concentration, the fluorescence intensity of B/R-CDs at 460 nm decreased, while that at 615 nm kept stable. Therefore, the fluorescence color of B/R-CDs changed from blue to red. By using the portable sensor to collect RGB value of fluorescence color, the R/B channel values showed a linear relationship with nitrite concentration in 2.5–600 µM, with detection limit of 0.8 µM. Then the fluorescence sensor was used to detect nitrite in preserved meat and pickles, and recovery rate was among 94.0%−105%. The detection results were consistent with those of fluorescence method and spectrophotometry. This work provides a novel detection device for on-site analysis, and also offers an effective approach for developing miniature fluorescence sensors.

Smartphone-based portable fluorescence sensor with gold nanoparticle mediation for selective detection of nitrite ions

A simple, portable device for the detection of NO2– via a fluorescence method was developed. The proposed device consisted of a dark box containing a blue LED as a low-power excitation light source and a smartphone with a mobile application for RGB analysis as a light detector. Detection was mediated by using synthesized cetyltrimethylammonium bromide-stabilized gold nanoparticles (CTAB-AuNPs). The CTAB-AuNPs were etched with NO2– to yield Au3+, which catalyzes the oxidation of o-phenylenediamine (OPD) in the presence of H2O2 to generate 2,3-diaminophenazine (DAP). Triton X-100 (TX-100) micelles were introduced to improve the DAP fluorescence emission. The fluorescence intensity of DAP was recorded by the smartphone in terms of RGB intensity, which was correlated with the NO2– concentration. This method provided a wide linear working concentration range (0.5–100 μM), a limit of detection of 0.17 μM and excellent selectivity for NO2– over other anions.

A sensitive and quantitative prognosis of C-reactive protein at picogram level using mesoporous silica encapsulated core-shell up-conversion nanoparticle based lateral flow strip assay

C- reactive protein (CRP) is a sensitive indicator for infectious or inflammatory diseases in human which can reflect the body's inflammation latency and early pathophysiological changes. The most common detection method of serum CRP is ELISA that has been proved to be expensive and time-consuming, restricting its use in point-of-care application. In this paper, we demonstrated a lateral flow system for CRP quantification by using mesoporous silica (mSiO2) coated up-converting nanoparticles (UCNPs) (denoted as UCNPs@mSiO2) as fluorescent labels. The up-converting core can emit strong green fluorescence signals under NIR excitation light (980 nm) with excellent photostability, high signal-to-noise ratio and low background fluorescence. By wrapping ultrathin mSiO2 outside, the core-shell structured UCNPs@mSiO2 exhibits good dispersity and stability meanwhile maintains strong fluorescence emission. Besides, the mSiO2 shell provides further functionalities for antibody linkage. By using a portable fluorescence sensor, we reached a CRP detection limit of 0.05 ng/mL and a linear range from 0.1 ng/mL-50 ng/mL, and the detection time was no more than 8 min. The lateral flow test strips exhibit great stability in CRP quantification (CV%<5) and have a life time of more than 1 week at ambient temperature. Furthermore, the proposed system can work with a cloud-enabled smartphone through Bluetooth for Internet of Medical Things application. This CRP detection method proves to be rapid and easy-operated, which has great potential in early inflammatory disease perception in the point-of-care tests and future's 5G-enabled remote healthcare management.

A donor-π-acceptor aggregation-induced emission compound serving as a portable fluorescent sensor for detection and differentiation of methanol and ethanol in the gas phase

The design strategy of aggregation-induced emission (AIE) fluorophores with donor-π-acceptor (D-π-A) conjugation structure has greatly contributed to the development of luminescent materials and devices, including volatile organic compounds (VOCs) sensors. In this work, a D-π-A fluorophore DEBAB was synthesized, showing both AIE and intramolecular charge transfer (ICT) properties as confirmed by spectroscopic data and quantum chemical calculations. Furthermore, there is notable emission-enhancement when DEBAB is exposed to small-molecule alcohols, such as methanol and ethanol. Based on this phenomenon, a portable film sensor was fabricated, capable of detecting methanol and ethanol in gas phase, with detection limit (DL) as low as 8.02 ppm. Our systematic investigation suggests that hydrogen-bonding may be formed between DEBAB and alcohols, intensifying the AIE efficacy while influencing the ICT process. This working mechanism is supported by density functional theory (DFT) calculations including electrostatic potential mapping and molecular total energy. In addition, a sensor array was fabricated on a cellulose paper strip, showing different levels of emission changing in response to alcohols. Thus the detection and differentiation of methanol and ethanol are enabled.

A portable and high-sensitivity optical sensing system for detecting fluorescently labeled enterohaemorrhagic Escherichia coli Shiga toxin 2B-subunit.

We developed a stand-alone, real-time optical detection device capable of reading fluorescence intensities from cell samples with high sensitivity and precision, for use as a portable fluorescent sensor for sensing fluorescently labeled enterohemorrhagic Escherichia coli (EHEC) Shiga toxins (Stxs). In general, the signal intensity from the fluorescently labeled Stxs was weak due to the small number of molecules bound to each cell. To address this technical challenge, we used a highly sensitive light detector (photomultiplier tube: PMT) to measure fluorescence, and designed a portable optical housing to align optical parts precisely; the housing itself was fabricated on a 3D printer. In addition, an electric circuit that amplified PMT output was designed and integrated into the system. The system shows the toxin concentration in the sample on a liquid crystal display (LCD), and a microcontroller circuit is used to read PMT output, process data, and display results. In contrast to other portable fluorescent detectors, the system works alone, without any peripheral computer or additional apparatus; its total size is about 17 × 13 × 9 cm3, and it weighs about 770 g. The detection limit was 0.01 ppm of Alexa Fluor 488 in PBS, which is ten thousand times lower than those of other smartphone-based systems and sufficiently sensitive for use with a portable optical detector. We used the portable real-time optical sensing system to detect Alexa Fluor 488–tagged Stx2B-subunits bound to monocytic THP-1 cells expressing the toxin receptor globotriaosylceramide (Gb3). The device did not detect a signal from Gb3-negative PD36 cells, indicating that it was capable of specifically detecting Stxs bound to cells expressing the toxin receptor. Following the development of a rapid and autonomous method for fluorescently tagging cells in food samples, the optical detection system described here could be used for direct detection of Shiga toxins in food in the field.

Fluorescence-Sensor Mapping for the in Vineyard Non-Destructive Assessment of Crimson Seedless Table Grape Quality.

Non-destructive tools for the in situ evaluation of vine fruit quality and vineyard management can improve the market value of table grape. We proposed a new approach based on a portable fluorescence sensor to map the ripening level of Crimson Seedless table grape in five different plots in the East, Central-North and South of the Macedonia Region of Greece. The sensor provided indices of ripening and color such as SFRR and ANTHRG correlated to the chlorophyll and anthocyanin berry contents, respectively. The mean ANTHRG index was significantly different among all the plots examined due to the occurrence of different environmental conditions and/or asynchronous ripening processes. The indices presented moderate, poor in some cases, spatial variability, probably due to a significant vine-to-vine, intra-vine and intra-bunch variability. The cluster analysis was applied to the plot with the most evident spatial structure (at Kilkis). Krigged maps of the SFRR, ANTHRG and yield were classified by k-means clustering in two-zones that differed significantly in their mean values. ANTHRG and SFRR were inversely correlated over 64% of the plot. SFRR appeared to be a potential useful proxy of yield since it was directly correlated to yield over 66% of the plot. The grape color (ANTHRG) was slightly higher over the low-yield zones with respect to the high-yield zones. Our study showed that the combination of anthocyanins and chlorophyll indices detected in the field on Crimson Seedless table grape by a portable fluorescence sensor can help in defining the best harvest time and the best areas for harvesting.

Feasibility of a point-of-care test based on quantum dots with a mobile phone reader for detection of antibody responses.

We developed a novel and portable fluorescent sensor that integrates a lateral flow assay with a quantum dot (Qdots) label and a mobile phone reader for detection of specific antibodies in human serum. We evaluated the utility of this assay to test for antibodies to the Taenia solium rT24H antigen. It was a retrospective study by examining 112 positive human sera from patients with neurocysticercosis (NCC) including samples from patients with single viable cyst (n = 18), two or more viable cysts (n = 71), and subarachnoid (racemose) cysts (n = 23). These samples were collected from previous study subjects in Lima, Peru under an approved study protocol in Peru. The sera were made anonymous under a protocol approved by the CDC Institutional Review Board. Definitive diagnosis of the subject was established by computed-tomography and/or magnetic resonance imaging. To test the specificity of the assay, we evaluated a panel of serum samples obtained from patients with other infections (n = 24), and serum samples from persons in the United States and Egypt who had not traveled outside their country, and therefore are presumed negative for cysticercosis (n = 128). The assay specificity in the negative panel was 99% (95–100%) while assay sensitivity was 89% (79–95%) in NCC patients with two or more viable cysts. Our assay has performance characteristics similar to those of traditional platforms for the detection of NCC and shows promise as a mobile phone reader-based point-of-care test for antibody detection.

A hand-held fluorescent sensor platform for selectively estimating green algae and cyanobacteria biomass

This paper reports a portable fluorescent sensor platform containing multiple excitation light illumination for quantification and differentiation of multiple analytes. The fluorescent sensor platform utilizes: (i) three different wavelengths of light emitting diodes (LEDs) for selectively stimulating target analytes; (ii) a sensitive photodetector for corresponding fluorescence measurements; (iii) a custom-built electronic system for data measurement and storage; and (iv) a compact three-dimensional printed housing for the developed sensor platform. Based on the fluorescent emission pattern obtained from each target analyte, multivariate analytical methods were applied to differentiate one analyte from the other in a mixture of multiple analytes. The fluorescent sensor platform was tested to selectively detect two target phytoplankton species: Chlorella vulgaris and Spirulina. Fluorescent emission of phytoplankton is caused by stimulation of photosynthetic pigments and is widely utilized to quantify and classify phytoplankton groups. Biomass estimation was therefore conducted by measuring chlorophyll a fluorescence emission for green algae (Chlorella vulgaris) using blue LED excitation and phycocyanin fluorescence emission for cyanobacteria (Spirulina) using amber LED excitation. The results demonstrated the viability of the developed device as a portable generic fluorescence sensor platform for simultaneously detecting various biochemical analytes.

Enhancing Sensitivity of Novel Hg2+ Fluorescent Sensor via Plasmonic Enhancement of Silver Nanoparticles

Abstract Contamination of Hg2+ in an aqueous environment is dangerous for all living species including human. In this work, a new rhodamine B derivative fluorescent sensor (sensor RBS) for Hg2+ detection was successfully synthesized. In addition, the synthesized yellow silver nanoparticles (Y-AgNPs) were incorporated into sensor RBS to obtain sensor RBS + Y-AgNPs. The sensitivity studies for Hg2+ detection of the sensors showed that the Hg2+ detection limit of sensor RBS and sensor RBS + Y-AgNPs were 12.9 ppb and 0.7 ppb, respectively. The result indicated that incorporation of Y-AgNPs into sensor RBS led to significantly lower Hg2+ detection limit of sensor RBS + Y-AgNPs, which could be attributed to plasmonic enhancement of Y-AgNPs. Furthermore, the selectivity studies of the sensors showed that sensor RBS and sensor RBS + Y-AgNPs were highly selective toward Hg2+ against interference ions. We also showed that sensor RBS + Y-AgNPs could be used to detect Hg2+ in real samples. Importantly, we have demonstrated that utilization of plasmonic enhancement could improve the sensitivity of the Hg2+ fluorescent sensor, which could pave the way for development of portable fluorescent sensor for the on-site Hg2+ detection.

A portable fluorescent sensor for on-site detection of microalgae

This work reports the development of a portable and low cost fluorescent sensing system with a disposable microfluidic chip for on-site detection of a microalgal sample and its concentration. The sensor system has multiple light emitting diodes (LEDs) for excitation and a photodetector for measuring a fluorescent signal from a microalgal sample. The concentration of a microalgal sample is determined by measuring the fluorescent signal emitted by chlorophyll a. A dichroic filter and a color filter are also added to allow only the fluorescent signal from chlorophyll a to pass through the photodetector. The microfluidic chip consists of a glass slide and a PDMS channel with a vacuum pump, which collects a small volume of the microalgal sample (<10μl). The fluorescent sensor was characterized with varying concentration of microalgal samples and demonstrated its capability of measuring microalgal concentrations. The sensor was also tested with microalgal samples mixed with different turbidity water to validate its selectivity. The results show that the fluorescent detection of microalgal concentration is not influenced by the turbidity level of the sample solution. The developed system can be used for on-site screening and monitoring of microalgal population with an integrated excitation and detection circuitry.

Highly portable fluorescent turn-on sensor for sulfide anions based on silicon nanowires

A portable fluorescent sensor for S2− based on SiNW arrays was realized and used to monitor S2− in running water.

Investigation of Leaf Diseases and Estimation of Chlorophyll Concentration in Seven Barley Varieties Using Fluorescence and Hyperspectral Indices

Leaf diseases, such as powdery mildew and leaf rust, frequently infect barley plants and severely affect the economic value of malting barley. Early detection of barley diseases would facilitate the timely application of fungicides. In a field experiment, we investigated the performance of fluorescence and reflectance indices on (1) detecting barley disease risks when no fungicide is applied and (2) estimating leaf chlorophyll concentration (LCC). Leaf fluorescence and canopy reflectance were weekly measured by a portable fluorescence sensor and spectroradiometer, respectively. Results showed that vegetation indices recorded at canopy level performed well for the early detection of slightly-diseased plants. The combined reflectance index, MCARI/TCARI, yielded the best discrimination between healthy and diseased plants across seven barley varieties. The blue to far-red fluorescence ratio (BFRR_UV) and OSAVI were the best fluorescence and reflectance indices for estimating LCC, respectively, yielding R2 of 0.72 and 0.79. Partial least squares (PLS) and support vector machines (SVM) regression models further improved the use of fluorescence signals for the estimation of LCC, yielding R2 of 0.81 and 0.84, respectively. Our results demonstrate that non-destructive spectral measurements are able to detect mild disease symptoms before significant losses in LCC due to diseases under natural conditions.

Quantum Dot-Based Immunochromatographic Fluorescent Biosensor for Biomonitoring Trichloropyridinol, a Biomarker of Exposure to Chlorpyrifos

A novel and portable fluorescent sensor that integrates an immunochromatographic test strip assay (ITSA) with a quantum dot (QD) label and a test strip reader was described in this study for simple, rapid, and sensitive biomonitoring of an organophosphorus pesticide metabolite. The principle of this sensor is based on a competitive immunoreaction that was performed on an immunochromatographic test strip, where analytes compete with competitors (QD-conjugated analogs) to bind to antibodies on a test zone. Captured QDs serve as signal vehicles for fluorescent readout. In this work, 3,5,6-trichloropyridinol (TCP) is used as a model analyte to demonstrate the performance of the immunosensor. QD-TCP conjugates were synthesized and characterized with X-ray photoelectron spectroscopy (XPS) and fluorescence spectroscopy. Some parameters (e.g., the amount of QD-modified TCP and immunoreaction time) that govern sensitivity and reproducibility of ITSA were optimized. Under optimal conditions, the sensor has a wide dynamic range and is capable of detecting a minimum 1.0 ng/mL TCP standard analyte in 15 min. The sensor has been successfully applied for detection of TCP spiked in rat plasma with average recovery of 102.0%. Results demonstrate that this sensor provides a rapid, clinically accurate, and quantitative tool for TCP detection and shows great promise for in-field and point-of-care (POC) quantitative testing and screening for metabolite biomarkers, e.g., TCP, for humans exposed to pesticides.

Selective fluoride sensing using organic–inorganic hybrid nanomaterials containing anthraquinone

Anthraquinone-based fluorescent receptor 1 was immobilized on mesoporous silica (AFMS) or on silica particles (AFSP) via a sol–gel reaction. The sensing abilities of AFMS and AFSP were studied by addition of the anions F−, Cl−, Br−, I− and HSO4− to water suspensions of the assayed solid. The addition of fluoride ions to a suspension of AFMS resulted in a large decrease in the fluorescence intensity of the anthraquinone of AFMS. Thus, fluoride ions bind to two urea N–H protons of receptor 1 in AFMS. In contrast, the addition of Cl−, Br−, I− or HSO4− did not reduce the fluorescence of AFMS. In the case of AFSP, the sensitivity for fluoride ions was 10 times lower than that of AFMS due to the immobilization of smaller amounts of receptor 1 on the silica particles. A linear response of AFMS upon the addition of fluoride ions was observed between 0.50 μM and 10.0 μM, with a detection limit of ∼0.50 μM. These results suggest that mesoporous silica with its large surface area is useful as a supporting material. Furthermore, receptor 1 was also immobilized on a glass slide surface by a sol–gel reaction. The fluorescence of 1 immobilized on a glass slide was quenched when dipped into F− solution. On the other hand, no fluorescence change was observed in Cl− solution. These results imply that 1 immobilized on a glass slide is applicable as a portable fluorescent sensor for detection of fluoride ions in the biological and environmental fields.