Fluorescent Sensor Array Research Articles

Ultrasensitive detection of aliphatic nitro-organics based on “turn-on” fluorescent sensor array

The broad class of explosives includes nitro aromatics as well as challenging aliphatic nitro-organics whose detection is important from counter-terrorism and national security perspectives. Here we report a turn-on fluorescent sensor array based on aggregation-induced emission (AIE) fluorophores as receptors. To achieve a good sensing system with fast response, good sensitivity and low detection limit, three receptors with abundant chemical diversities for target analytes were synthesized. The turn-on response of the individual receptor showed highly variable and cross-reactive analyte-dependent changes in fluorescence. The excellent ability to identify a variety of explosives, especially the challenging aliphatic nitro-organics (2,3-dimethyl-2,3-dinitrobutane (DMNB), 1,3,5-trinitro-1,3,5-triazinane (RDX), cyclotetramethylene tetranitramine (HMX) and entaerythritol tetranitrate (PETN)), was demonstrated in qualitative and quantitative analyses with 100% accuracy. The fluorescence signal amplification in the presence of explosives allows for application of these receptors in a sensor microarray suitable for high-throughput screening. These results suggested that the cross-reactive sensor array based on AIE fluorophores could find a wide range of applications for sensing various analytes or complex mixtures.

Detection of ammonia based on a novel fluorescent artificial nose and pattern recognition

A simple and rapid fluorescent sensor array for identification and quantification of different concentrations (ppb level) of ammonia was proposed in this paper. Employing porphyrin, porphyrin derivative and chemically responsive dyes as the sensing elements, the developed sensor array of artificial nose showed a unique pattern of fluorescence changes upon its exposure to ammonia for just 4 min. And the eigenvalues from raw fluorescence spectra were analyzed by means of pattern recognition algorithm, including hierarchical cluster analysis (HCA), principal component analysis (PCA) and back-propagation neural network (BPNN). The results showed that HCA and PCA, which were used to assess the feasibility and effectiveness of discrimination of fluorescent sensor array, revealed a distinct separation between samples. BPNN were used for automatically classifying and predicting concentration of ammonia, and the accuracy was 97.55% while the relative standard deviation (RSD) was up to 3.67% for real samples. It indicates the fluorescent artificial nose system is a rapid and feasible sensing platform for the identification and quantitative analysis of gases, and also shows the possibilities in the field of environmental gas detection and environmental gas monitoring.

Fluorescence sensor array for identification of commercial milk samples according to their thermal treatments

Identification of processed milk is of importance for commercial and legal concerns. The fluorescence response patterns induced by fluorophore/protein interactions allow a possible discrimination of processed milk samples corresponding to their thermal treatment. The fluorescence responses of 4 fluorophores upon addition of commercial milk samples in 96-well plate are measured in the range of 400–600nm using the excitation wavelength at 375nm. The pattern recognition of the 53,126 fluorescence responses (4 fluorophores×41 wavelengths×4 thermally processed milks×3 brands×3 lots×3 bottles×3 repeats) are analyzed by multivariate statistical methods. Linear discriminant analysis (LDA) successfully recognizes the milk samples according to their thermal processing, i.e. pasteurized milk, sterilized milk, UHT fresh milk and recombined milk (UHT milk having milk powder), with 100% classification accuracy in a cross validation using a leave-one-out technique.

Suspension Array of Ionic Liquid or Ionic Liquid-Quantum Dots Conjugates for the Discrimination of Proteins and Bacteria.

It is of great importance to develop novel and sensitive sensing materials for the detection of proteins and microorganisms to fulfill the demand of disease diagnosis. As the selectivity and sensitivity of sensing systems are highly dependent on the receptor, the fluorescent sensor array with imidazolium ionic liquids (ILs) and ionic liquid-quantum dots conjugates as semiselective receptors is developed for protein/bacteria differential sensing or discrimination. The IL sensing system formed by 1,3-dibutylimidazolium chloride (BBimCl), 1,3-diethylimidazolium bromine (EEimBr), 1,3-dibutylimidazolium bromine (BBimBr), 1,3-dihexylimidazolium bromine (HHimBr), and 1,3-dioctylimidazolium bromine (OOimBr) and the IL@QDs/QDs sensing system formed by CdTe, BBimCl@CdTe, EEimBr@CdTe, BBimBr@CdTe, and HHimBr@CdTe are tested, by transferring the interaction binding difference between receptors and proteins to the fluorescent response pattern. The IL sensing system is applied to the identification of 48 samples (8 proteins at 500 nM) with an accuracy of 91.7%. For the IL@QDs/QDs sensing system, 8 proteins are completely distinguished with 100% accuracy at a very low concentration level of 10 nM. Remarkably, 36 training cases (6 strains of bacteria from 3 different species) are discriminated with 100% (OD600 of 0.1).

Mechanism of Immobilized Protein A Binding to Immunoglobulin G on Nanosensor Array Surfaces

Protein A is often used for the purification and detection of antibodies such as immunoglobulin G (IgG) because of its quadrivalent domains that bind to the Fc region of these macromolecules. However, the kinetics and thermodynamics of the binding to many sensor surfaces have eluded mechanistic description due to complexities associated with multivalent interactions. In this work, we use a near-infrared (nIR) fluorescent single-walled carbon nanotube sensor array to obtain the kinetics of IgG binding to protein A, immobilized using a chelated Cu(2+)/His-tag chemistry to hydrogel dispersed sensors. A bivalent binding mechanism is able to describe the concentration dependence of the effective dissociation constant, KD,eff, which varies from 100 pM to 1 μM for IgG concentrations from 1 ng mL(-1) to 100 μg mL(-1), respectively. The mechanism is shown to describe the unusual concentration-dependent scaling demonstrated by other sensor platforms in the literature as well, and a comparison is made between resulting parameters. For comparison, we contrast IgG binding with that of human growth hormone (hGH) to its receptor (hGH-R) which displays an invariant dissociation constant at KD = 9 μM. These results should aid in the use of protein A and other recognition elements in a variety of sensor types.

Simple and Sensitive Discrimination of Amino Acids with Functionalized Silver Nanoparticles.

A chemiluminescence (CL) sensing method for amino acid discrimination based on luminol functionalized silver nanoparticles (LumAgNPs) has been developed. Luminescence emission in the presence of hydrogen peroxide under neutral conditions was characterized in three ways: the time required for the signal to appear (Ta), the time required to reach maximum luminescence (Tp), and CL intensity. These factors were found to change upon interaction of the nanoparticles with various amino acids, leading to distinct response patterns characteristic of each analyte. Seven amino acids (l-cysteine, l-proline, l-phenylalanine, l-arginine, l-threonine, l-glutamic acid, and l-tyrosine) were identified at a concentration of 10 ng/mL. This sensitivity is about 3 orders of magnitude better than that of recently reported methods based on fluorescent sensor arrays using cucurbit[n]uril and comparable to high-performance liquid chromatography. Application to 27 unknown samples gave a 96.3% success rate at the 10 ng/mL level.

A novel device based on a fluorescent cross-responsive sensor array for detecting lung cancer related volatile organic compounds.

In this paper, a novel, simple, rapid, and low-cost detection device for lung cancer related Volatile Organic Compounds (VOCs) was constructed. For this task, a sensor array based on cross-responsive mechanism was designed. A special gas chamber was made to insure sensor array exposed to VOCs sufficiently and evenly, and FLUENT software was used to simulate the performance of the gas chamber. The data collection and processing system was used to detect fluorescent changes of the sensor arrays before and after reaction, and to extract unique patterns of the tested VOCs. Four selected VOCs, p-xylene, styrene, isoprene, and hexanal, were detected by the proposed device. Unsupervised pattern recognition methods, hierarchical cluster analysis and principal component analysis, were used to analyze data. The results showed that the methods could 100% discriminate the four VOCs. What is more, combined with artificial neural network, the correct rate of quantitative detection was up to 100%, and the device obtained responses at concentrations below 50 ppb. In conclusion, the proposed detection device showed excellent selectivity and discrimination ability for the VOCs related to lung cancer. Furthermore, our preliminary study demonstrated that the proposed detection device has brilliant potential application for early clinical diagnosis of lung cancer.

Fluorescence sensor arrays for identification of foodborne pathogens

A fluorescence sensor array containing polyelectrolyte fluorophores has been developed for foodborne pathogen detection and identification.

Bispyrene/surfactant-assembly-based fluorescent sensor array for discriminating lanthanide ions in aqueous solution.

Lanthanides are valuable nonrenewable resources and widely used in a variety of industries. Detection and identification of lanthanide ions are in high demand but challenging because of the similarity among lanthanide ions. In the present work, a fluorescent sensor array of three cationic bispyrene derivatives mixed with anionic surfactant assemblies was developed. The sensor array exhibits cross-reactive responses to lanthanide ions when tested in aqueous solution. The combination of fluorescence variations at both monomer and excimer emission of each of the bispyrene sensor elements provides a six-signal recognition pattern for lanthanide ions. Principle component analysis illustrates that the sensor array could at least identify 6 of the 14 similar lanthanide ions including La(3+), Pr(3+), Nd(3+), Eu(3+), Ho(3+), and Er(3+). UV-vis absorption measurements rule out the possibility of binding lanthanides with fluorophores. Fluorescence titration experiments in both cationic and neutral surfactant aqueous solutions reveal that the three fluorophores show slight fluorescence responses to the lanthanide ions, indicating that electrostatic attraction between lanthanide ions and anionic surfactant plays an important role in the sensing behavior of the sensor array. Control experiments with divalent metal ions find no cross-reactive responses, suggesting that the stronger electrostatic interaction with trivalent lanthanide ions is responsible for the multiple fluorescence responses.

An artificial tongue fluorescent sensor array for identification and quantitation of various heavy metal ions.

Herein, a small-molecule fluorescent sensor array for rapid identification of seven heavy metal ions was designed and synthesized, with its sensing mechanism mimicking that of a tongue. The photoinduced electron transfer and intramolecular charge transfer mechanism result in combinatorial interactions between sensor array and heavy metal ions, which lead to diversified fluorescence wavelength shifts and emission intensity changes. Upon principle component analysis (PCA), this result renders clear identification of each heavy metal ion on a 3D spatial dispersion graph. Further exploration provides a concentration-dependent pattern, allowing both qualitative and quantitative measurements of heavy metal ions. On the basis of this information, a "safe-zone" concept was proposed, which provides rapid exclusion of versatile hazardous species from clean water samples based on toxicity characteristic leaching procedure standards. This type of small-molecule fluorescent sensor array could open a new avenue for multiple heavy metal ion detection and simplified water quality analysis.

Discrimination of fresh fruit juices by a fluorescent sensor array for carboxylic acids based on molecularly imprinted titania

Design of chemical sensor arrays that can discriminate real-world samples has been highly attractive in recent years. Herein a fluorescent indicator-displacement sensor array for discrimination of fresh fruit juices was developed. By coupling the unique high affinity of titania to electron-donating anions and the cross-reactivity of molecularly imprinted materials to structurally similar species, a small array was fabricated using only one rhodamine-based fluorescent dye and three synthesized materials. Citric, malic, succinic and tartaric acids were chosen as indices. The recognition mechanism was investigated by spectrofluorimetric titration using a non-linear Langmuir-type adsorption model. The proposed method was applied to discriminate thirteen fruit juices through their carboxylic acid contents. Principal component analysis of the data clearly grouped the thirteen juices with the first principal component owning 98.2% of the total variation. The comparison of the sensor array with HPLC determination of the carboxylic acids was finally made.

“Turn-on” fluorescent sensor array for basic amino acids in water

Amino acids and their derivatives are recognized and analyzed in water using a turn-on fluorescent cucurbituril based sensor array. Multivariate analysis (LDA and HCA) clearly shows that the sensor array can discriminate amino acids from the corresponding amines which are produced by the action of amino acid decarboxylases.

Multiple fluorescence ΔCIE and ΔRGB codes for sensing volatile organic compounds with a wide range of responses

A highly luminescent compound, stilbene-2,4-dimethyl-6-(1,2,2,4-tetramethyl-1,2-dihydroquinolin-6-yl)-1,3,5-s-triazine (MQT), exhibits solvent polarity-induced emission enhancement. A fluorescent sensor array was fabricated with MQT and porous polymer substrates. The colorimetric changes of the array exposed to VOCs can be readily distinguished by the naked eye. Post-processing procedures proved the high selectivity of the array for VOCs.

Fluorescent Polymer Sensor Array for Detection and Discrimination of Explosives in Water

A fluorescent polymer sensor array (FPSA) was made from commercially available fluorescent polymers coated onto glass beads and was tested to assess the ability of the array to discriminate between different analytes in aqueous solution. The array was challenged with exposures to 17 different analytes, including the explosives trinitrotoluene (TNT), tetryl, and RDX, various explosive-related compounds (ERCs), and nonexplosive electron-withdrawing compounds (EWCs). The array exhibited a natural selectivity toward EWCs, while the non-electron-withdrawing explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) produced no response. Response signatures were visualized by principal component analysis (PCA), and classified by linear discriminant analysis (LDA). RDX produced the same response signature as the sampled blanks and was classified accordingly. The array exhibited excellent discrimination toward all other compounds, with the exception of the isomers of nitrotoluene and aminodinitrotoluene. Of particular note was the ability of the array to discriminate between the three isomers of dinitrobenzene. The natural selectivity of the FPSA toward EWCs, plus the ability of the FPSA to discriminate between different EWCs, could be used to design a sensor with a low false alarm rate and an excellent ability to discriminate between explosives and explosive-related compounds.

Protein discrimination by fluorescent sensor array constituted of variously charged dendritic phenylene–ethynylene fluorophores

A protein fluorescent sensor array based on variously charged dendritic fluorophores is developed. The variation of charge is achieved by different combinations of cationic trimethylammonium, anionic carboxylate and non-ionic methyl ester or N,N-dimethylamino on the peripheries of the fluorophores. Nine phenylene–ethynylene dendritic fluorophores, seven zeroth generation bearing charges varied from −3 to +3 and two first generation bearing −6 and +6 charges, are synthesized from triiodotriphenylamine through series of Sonogashira coupling. In phosphate buffer saline pH 7.4, five out of these nine compounds fluorogenically response to eight protein analytes distinctively. The data set of fluorescent intensities obtained from 5 fluorophores × 8 proteins × 9 replicated measurements can be statistically sorted into eight clusters corresponding to each protein by principal component analysis (PCA). Factorial discriminant analysis (FDA) cross-validation is applied to locate the optimum detection wavelength and reduce the number of sensing elements from nine to two with 100% discriminating accuracy. The method described should be generally practical for the development of electronic tongue for protein related food analysis and medical diagnosis.

Discrimination of Saccharides with a Fluorescent Molecular Imprinting Sensor Array Based on Phenylboronic Acid Functionalized Mesoporous Silica

A fluorescent indicator-displacement molecular imprinting sensor array based on phenylboronic acid functionalized mesoporous silica was developed for discriminating saccharides. D-Fructose imprinted material (FruIM), D-xylose imprinted material (XylIM) together with a control blank nonimprinted material (NIM) were synthesized as the elements of the imprinting sensor array. Spectrofluorimetric titrations of the three materials with eight selected saccharides were carried out, and Stern-Volmer quenching constants (K(SV)) of NIM, FruIM, and XylIM with the eight selected saccharides were obtained to investigate the interaction of the materials with saccharides. The present approach couples molecular imprinting technique to indicator-displacement strategy with the use of one conventional saccharide receptor (phenylboronic acid) and one commercially available fluorescent dye (Alizarin Red S., ARS) as the indicator, and allows identifying two template saccharides (D-fructose and D-xylose) plus eight nontemplate saccharides (D-arabinose, D-glucose, D-galactose, D-mannose, L-sorbose, D-ribose, L-rhamnose and sucrose). The principal component analysis (PCA) plot shows a clear discrimination of the 10 tested saccharides at 100 mM and the first principal component possesses 94.8% of the variation. Besides, the developed saccharide imprinted sensor array is successfully applied to discriminating three brands of orange juice beverage.

A fluorescent sensor array based on ion imprinted mesoporous silica

We report an ion imprinted mesoporous silica based fluorescence turn-on sensor array for discrimination of metal ions. A novel fluorescent functional monomer containing an 8-hydroxyquinoline (8-HQ) moiety in combination with one-pot co-condensation method was employed to prepare fluorescent ion imprinted mesoporous silica. The imprinted materials for Zn 2+ and Cd 2+ as well as a control blank non-imprinted material (NIM) were synthesized. With the covalently anchored organic fluorophore in the inorganic mesoporous silica matrix, the binding of metal ions to the imprinting site was directly transformed into fluorescence signals. Both the imprinted materials displayed faster binding kinetics toward metal ions than NIM. Apparent binding constants (adsorption constants) for the materials with the metal ions in water were determined by a Langmuir-type analysis of the spectrofluorimetric titration data. The sensor array composed of the three materials allows discriminating the two template metal ions (Zn 2+ and Cd 2+) plus three non-template metal ions (Mg 2+, Ca 2+ and Al 3+) at two different concentrations. This work proves that using a simple fluorescent receptor can provide a pattern based fluorescent sensing system by taking advantage of the imprinting effect.

Fluorescence Sensor Array for Metal Ion Detection Based on Various Coordination Chemistries: General Performance and Potential Application

A sensor array containing 9 cross-reactive sensing fluorescent elements with different affinity and selectivity to 10 metal cations (Ca(2+), Mg(2+), Cd(2+), Hg(2+), Co(2+), Zn(2+), Cu(2+), Ni(2+), Al(3+), Ga(3+)) is described. The discriminatory capacity of the array was tested at different ranges of pH and at different cation concentrations using linear discriminant analysis (LDA). Qualitative identification of cations can be determined with over 96% of accuracy in a concentration range covering 3 orders of a magnitude (5-5000 microM). Quantitative analysis can be achieved with over 90% accuracy in the concentration range between 10 and 5000 microM. The array performance was also tested in identification of nine different mineral water brands utilizing their various electrolyte compositions and their Ca(2+), Mg(2+), and Zn(2+) levels. LDA cross-validation routine shows 100% correct classification for all trials. Preliminary results suggest that similar arrays could be used in testing of the consistency of the purification and manufacturing process of purified and mineral waters.

Rational Design of a Minimal Size Sensor Array for Metal Ion Detection

The focus of this study was to demonstrate that, in the luminescent sensors, the signal transduction may possibly be the most important part in the sensing process. Rational design of fluorescent sensor arrays for cations utilizing extended conjugated chromophores attached to 8-hydroxyquinoline is reported. All of the optical sensors utilized in the arrays comprise the same 8-hydroxyquinoline (8-HQ) receptor and various conjugated chromophores to yield a different response to various metal cations. This is because the conjugated chromophores attached to the receptor are partially quenched in their resting state, and upon the cation coordination by the 8-HQ, the resulting metalloquinolinolate complex displays a change in fluorescence. A delicate balance of conjugation, fluorescence enhancement, energy transfer, and a heavy metal quenching effect results in a fingerprint-like pattern of responses for each sensor-cation complex. Principal component analysis (PCA) and linear discriminant analysis (LDA) are used to demonstrate the contribution of individual sensors within the array, information that may be used to design sensor arrays with the smallest number of sensor elements. This approach allows discriminating between 10 cations by as few as two or even one sensor element. Examples of arrays comprising various numbers of sensor elements and their utility in qualitative identification of Ca(2+), Mg(2+), Cd(2+), Hg(2+), Co(2+), Zn(2+), Cu(2+), Ni(2+), Al(3+), and Ga(3+) ions are presented. A two-member array was found to identify 11 analytes with 100% accuracy. Also the best two of the sensors were tested alone and both were found to be able to discriminate among the samples with 99% and 96% accuracy, respectively. To illustrate the utility of this approach to a real-world application, identification of enhanced soft drinks based on their Ca(2+), Mg(2+), and Zn(2+) cation content was performed. The same approach to reducing array elements was used to construct three- and two-member arrays capable of identifying these complex analytes with 100% accuracy.

“Click-fluors”: Modular Fluorescent Saccharide Sensors Based on a 1,2,3-Triazole Ring

A carbohydrate sensing "click-fluor" is reported which displays a nontypical binding preference with sample saccharides. That a fluorescent sensor is generated as a result of triazole formation (click reaction), rather than simply bringing the sensor and reporter units together via a triazole linkage, and the potential applicability of the wide range of easily accessible acetylene units means a simple strategy for the development of modular fluorescent sensor arrays for rapid screening of target saccharides will be available.