Sensitive and selective plasmonic assay for spermine as biomarker in human urine

Multiplex Detection of Biogenic Amines for Meat Freshness Monitoring Using Nanoplasmonic Colorimetric Sensor Array

Biogenic amines (BAs) were presented as significant markers for the evaluation of the spoilage of meat and meat products. In this work, a colorimetric sensor array was developed for the discrimination and detection of spermine (SP), spermidine (SD), histamine (HS), and tryptamine (TP) as important BAs in food assessment. For this aim, two important spherical plasmonic nanoparticles, namely gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs), were utilized as the sensing elements of the probes. The cross-reactive interaction of the target biogenic amines and the plasmonic nanoparticles caused the aggregation-induced UV-Vis spectra changes, which were accompanied by visual color variation in the solution. The collected responses were analyzed by principal component analysis-linear discrimination analysis (PCA-LDA) to classify the four BAs. This colorimetric sensor array can also discriminate between the individual BAs and their mixture accurately. Partial least squares regression (PLS-R) was also utilized for quantitative analysis of the BAs. The wide linear concentration ranges of 0.1-10.0 µM for the four BAs and desirable figures of merits (FOMs) showed the potential of the developed sensor for quantitative detection of the BAs. Finally, the practical ability of the developed probe was studied by the determination of the BAs in the meat samples, which successfully proved the potential of the colorimetric sensor array in a food sample.

Application of gold nanoparticles to determine spermine in the presence of other polyamines

The development of methods for the detection of polyamines in biological fluids is essential to improve early diagnosis and treatment of patients with prostate cancer. One of the promising areas is the use of noble metal nanoparticles. According to the literature data, there is no methodological approach have been developed to reliably distinguish spermine from other polyamines, in particular, from their acetylated forms and related compounds present in biological fluids. The paper presents the results of spectrophotometric determination of spermine both alone and in the presence of putrescine, spermidine or urea in the urine using gold nanoparticles. The results of the experiments proved that the developed method is suitable for the selective determination of spermine. It was shown that the presence of spermidine, putrescine, acetylated forms of polyamines or carbamide does not affect the results of the analysis.

In-tube solid phase microextraction coupled to miniaturized liquid chromatography for both, noble metal nanoparticle assessment and sensitive plasmonic assay development

Colorimetric localized surface plasmon resonance (LSPR) as analytical response is applied for a wide number of chemical sensors and biosensors. However, the dependence of different factors, such as size distribution of nanoparticles (NPs), shape, dielectric environment, inter-particle distance and matrix, among others, can provide non-reliable results by UV-vis spectrometry in complex matrices if NP assessment is not carried out, particularly at low levels of analyte concentrations. Miniaturized liquid chromatography, capillary (CapLC) and nano (NanoLC), coupled on line with in-tube solid phase microextraction (IT-SPME) is proposed for the first time for both, controlling suitability of used noble metal NP dispersions and developing plasmonic assays. Several capped noble NPs and target analytes were tested from variations in the chromatographic profiles obtained by using diode array detection. The IT-SPME step, which influenced the chromatographic fingerprint provided by noble NP dispersions, was studied by asymmetrical flow field flow fractionation (AF4) too. We monitored NP aggregation induced by interaction with several analytes like acids and spermine (SPN). Assessment of NPs was achieved in less than 10 min and it permitted to develop suitable plasmonic tests. Here, it was also demonstrated that these assays can be followed by IT-SPME-miniaturized LC-DAD and more sensitivity and selectivity than those provided by UV-Vis spectrometry were achieved. Analysing urine samples to determine SPN as a cancer biomarker as a proof of concept is presented.

Providing Multicolor Plasmonic Patterns with Au@Ag Core-Shell Nanostructures for Visual Discrimination of Biogenic Amines

Biogenic amines (BAs) are known as substantial indicators of the quality and safety of food. Developing rapid and visual detection methods capable of simultaneously monitoring BAs is highly desired due to their harmful effects on human health. In the present study, we have designed a multicolor sensor array consisting of two types of gold nanostructures (i.e., gold nanorods (AuNRs) and gold nanospheres (AuNSs)) for the discrimination and determination of critical BAs (i.e., spermine (SM), tryptamine (TT), ethylenediamine (EA), tyramine (TR), spermidine (SD), and histamine (HT)). The design principle of the probe was based on the metallization of silver ions on the surface of AuNRs and AuNSs in the presence of BAs, forming Au@Ag core-shell nanoparticles. Changes in the surface composition, size, and aspect ratio of AuNSs and AuNRs induced a blue shift in the plasmonic band, which was accompanied by sharp and rainbowlike color variations in the solution. The collected data were visually assessed and statistically analyzed by various data visualization and pattern recognition methods. Namely, linear discriminant analysis (LDA) and partial least squares (PLS) regression were employed for the qualitative and quantitative determination of BAs. The responses were linearly correlated to the concentrations of BAs in a wide range of 10-800, 20-800, 40-800, 40-800, 60-800, and 80-800 μmol L^-1 with the limit of detections of 2.46, 4.79, 8.58, 14.26, 10.03, and 27.29 μmol L^-1 for SD, SM, TT, HT, EA, and TR, respectively. Finally, the practical applicability of the sensor array was investigated by the determination of BAs in meat and fish samples by which the potential of the probe for on-site determination of food freshness/spoilage was successfully verified.

Study of the Stability of Citrate Capped AgNPs in Several Environmental Water Matrices by Asymmetrical Flow Field Flow Fractionation

Asymmetrical flow field-flow fractionation (AF4) coupled to UV-Vis and dynamic light scattering (DLS) detectors in series, was tested for stability studies of dispersions of citrate-capped silver nanoparticles (AgNPs) in several water matrices. The main goal is to provide knowledge to understand their possible behavior in the environment for short times since mixturing (up to 180 min). Ultrapure (UPW), bottled (BW1, BW2), tap (TW), transitional (TrW) and sea water (SW) matrices were assayed. Observations were compatible with the aggregation of AgNPs, a change in the plasmon band and a size growth with time were done. Fractograms showed different evolution fingerprints in the function of the waters and batches. The aggregation rate order was BW2, SW, TrW, BW1 and TW, being BW2 the lowest and TW the highest. NP aggregation can be induced by increasing the salt concentration of the medium, however transitional and sea waters did not follow the rule. Both matrices presented a lower aggregation rate in comparison with other aqueous matrices with much lower ionic strength (BW1 and TW), which can be explained by the potential presence of dissolved organic matter and/or the high concentration of halides providing their stabilization and passivation, respectively. AF4 provides relevant information with respect to static DLS and UV-Vis Spectroscopy showing that at least two populations of aggregates with different sizes between them, depending on both, the mixture time for a given matrix and type of water matrix for the same time.

Chromogenic Chemodosimeter Based on Capped Silica Particles to Detect Spermine and Spermidine

A new hybrid organic–inorganic material for sensing spermine (Spm) and spermidine (Spd) has been prepared and characterized. The material is based on MCM-41 particles functionalized with an N-hydroxysuccinimide derivative and loaded with Rhodamine 6G. The cargo is kept inside the porous material due to the formation of a double layer of organic matter. The inner layer is covalently bound to the silica particles, while the external layer is formed through hydrogen and hydrophobic interactions. The limits of detection determined by fluorimetric titration are 27 µM and 45 µM for Spm and Spd, respectively. The sensor remains silent in the presence of other biologically important amines and is able to detect Spm and Spd in both aqueous solution and cells.

Silver Nanoparticles for a Colorimetric Determination of Putrescine and Cadaverine in Biological Samples

A convenient and uncomplicated scheme has been projected for the quantitative determination of essential diamines putrescine (PUT) and cadaverine (CAD) via sodium dodecyl sulfate protected silver nanoparticles (SDS-AgNPs). This scheme is based on the chemical interaction of a SDS-AgNPs probe with PUT and CAD, leading to a color change from yellow to red or reddish brown. The interaction was investigated through different techniques such as using a UV-visible spectrophotometer, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), dynamic light scattering spectroscopy (DLS) and the zeta potential. Both amines possess a close resemblance in structure (except for the addition of one more methylene group in CAD), and no any distinguishable color change was noted. However, the maximum absorption band at 580 and 600 nm was demonstrated for PUT and CAD correspondingly. The methodical response was observed at absorption ratios of 580/410 and 600/410 nm, with the linear regression within 4 - 12 and 6 - 14 μg/mL for PUT and CAD. The detection limits calculated for both the diamines PUT and CAD were 0.333 and 1.638 μg/mL. The scheme was successfully applied for determinations in biological samples, including spiked blood plasma and urine. Putrescine exhibited % recovery within 95.717 - 105.200%, while cadaverine was within 95.940 - 105.109%, respectively. The scheme was reproducible and precise with inter-day RSD (n = 5) within 1.126, 0.018% and the intraday RSD (n = 5) was within 0.005, 0.002% for PUT and CAD, respectively.

Aqueous Dilution of Noble NPs Bulk Dispersions: Modeling Instability due to Dissolution by AF4 and Stablishing Considerations for Plasmonic Assays

Among different nanomaterials, gold and silver nanoparticles (AuNPs and AgNPs) have become useful tools for a wide variety of applications in general, and particularly for plasmonic assays. Particle size and stability analysis are key elements for their practical applications since the NPs properties depend on these parameters. Hence, in the present work, asymmetrical flow field flow fractionation (AF4) coupled to UV-Vis and dynamic light scattering (DLS) detectors in series, has been evaluated for stability studies of citrate-capped AuNPs and AgNPs aqueous dispersions. First, experimental parameters, such as mobile phase or cross-flow rate were optimized. Sodium azide to pH 7 for AuNPs and pH 9.2 for AgNPs were selected as the optimum mobile phase. The analytical response of bulk dispersions of AuNPs (20, 40, 60 and 80 nm) and AgNPs (20, 40 and 60 nm) and their dilutions have been studied. Fractograms showed a decrease on the absorbance signal in diluted dispersions as a function of time and particle size for the diluted dispersions that can be explained by dissolution in diluted dispersion since hydrodynamic diameter was constant. The results indicated that the dependence of the signal with time was more intense for AgNPs than for AuNPs, which can be correlated with its lower stability. These findings should be considered when plasmonic assays are realized. Here, assays involving non-oxidant acidic acids as use cases, were tested for several batches of NPs and considerations about their stability and operability stablished.

Femtomolar Detection of Spermidine Using Au Decorated SiO2 Nanohybrid on Plasmon-Coupled Extended Cavity Nanointerface: A Smartphone-Based Fluorescence Dequenching Approach

Coupling of photons with molecular emitters in different nanocavities have resulted in transformative plasmonic applications. The rapidly expanding field of surface plasmon-coupled emission (SPCE) has synergistically employed subwavelength optical properties of localized surface plasmon resonance (LSPR) supported by nanoparticles (NPs) and propagating surface plasmon polaritons assisted by metal thin films for diagnostic and point-of-care analysis. Gold nanoparticles (AuNPs) significantly quench the molecular emission from fluorescent molecules (at close distances <5 nm). More often, complex strategies are employed for providing a spacer layer around the AuNPs to avoid direct contact with fluorescent molecules, thereby preventing quenching. In this study we demonstrate a rapid and facile strategy with the use of Au-decorated SiO₂ NPs (AuSil), a metal (Au)-dielectric (SiO₂) hybrid material for dequenching the otherwise quenched fluorescence emission from radiating dipoles and to realize 88-fold enhancement using the SPCE platform. Different loading of AuNPs were studied to tailor fluorescence emission enhancements in spacer, cavity, and extended (ext.) cavity nanointerfaces. We also present femtomolar detection of spermidine using this nanohybrid in a highly desirable ext. cavity interface. This interface serves as an efficient coupling configuration with dual benefits of spacer and cavity architectures that has been widely explored hitherto. The multifold hot-spots rendered by the AuSil nanohybrids assist in augmented electromagnetic (EM)-field intensity that can be captured using a smartphone-based SPCE platform presenting excellent reliability and reproducibility in spermidine detection.

Miniaturized liquid chromatography coupled on-line to in-tube solid-phase microextraction for characterization of metallic nanoparticles using plasmonic measurements. A tutorial

This tutorial aims at providing guidelines for analyzing metallic nanoparticles (NPs) and their dispersions by using methods based on miniaturized liquid chromatography with diode array detection (MinLC-DAD) and coupled on-line to in-tube solid-phase microextraction (IT-SPME). Some practical advice and considerations are given for obtaining reliable results. In addition, this work outlines the potential applications that set these methodologies apart from microscopy-related techniques, dynamic light scattering, single particle ICP-MS, capillary electrophoresis, field-flow fractionation and other chromatographic configurations, which are discussed and mainly seek to accomplish size estimation and NP separation, speciation analysis and quantification of mainly AgNPs and AuNPs. MinLC-DAD has the potential to estimate the NP concentration and from it the average size of unknown samples by calibrating with a single standard, as well as studying potentially non-spherical particles and stability-related properties of their dispersions. While keeping the signal dependency with concentration and increasing the method sensitivity, IT-SPME-MinLC-DAD goes further allowing for the assessment of the dispersant effect and ultimately changes in the nanoparticle surroundings that range from modifications of the hydrodynamic diameter to the exposure to different reagents and matrices. The methodology can still be improved by either exploring newer IT-SPME adsorbents or by assaying new system configurations. Taking into account that this technique gives complementary information in relation to other techniques discussed here, this tutorial serves as a guide for analyzing metallic NPs towards a better understanding of the particle behavior under different scenarios.

Chemosensors for biogenic amines and biothiols

There is burgeoning interest among supramolecular chemists to develop novel molecular systems to detect biogenic amines and bio-thiols in aqueous and non-aqueous media due to their potential role in biological processes. Biogenic amines are biologically important targets because of their involvement in the energy metabolism of human biological systems and their requirement is met through food and nutrition. However, the increasing instances of serious health problems due to food toxicity have raised the quality of food nowadays. Biogenic amines have been frequently considered as the markers or primary quality parameters of foods like antioxidant properties, freshness and spoilage. For instance, these amines such as spermine, spermidine, cadavarine, etc. may originate during microbial decarboxylation of amino acids of fermented foods/beverages. These amines may also react with nitrite available in certain meat products and concomitantly produce carcinogenic nitrosamine compounds. On the other hand, it is also well established that biothiols, particularly, thiol amino acids, provide the basic characteristics to food including flavor, color and texture that determine its acceptability. For instance, the reduction of thiol groups produces hydrogen sulfide which reduces flavour as in rotten eggs and spoiled fish, and the presence of hydrogen sulfide in fish is indicative of spoilage. Thus, biogenic amines and bio-thiols have attracted the profound interest of researchers as analytical tools for their quantification. Much scientific and technological information is issued every year, where the establishment of precise interactions of biogenic amines and bio-thiols with other molecules is sought in aqueous and non-aqueous media. This review summarizes the optical chemosensors developed for the selective detection of biogenic amines and bio-thiols.

Design and Characterization of Dicyanovinyl Reactive Dyes for the Colorimetric Detection of Thiols and Biogenic Amines

The synthesis of two new azobenzene dyes, namely CR-528 and CR-555, and their spectral properties in ethanol solution are described. The recognition of sulfur-containing analytes (2-mercaptoethanol (2-ME), sodium hydrosulfide (NaHS)), and biogenic amines (spermine, spermidine, ethanolamine) bestowed significant spectral changes with color changes from pink/purple to pale yellow/orange-yellow. The nitro acceptor group in the dicyanovinyl reactive dye contributes to higher sensitivity and lower detected analyte concentrations. The absorption maxima of both the dyes are at wavelengths compatible with low-cost light sources and detectors, making them excellent candidates for optical probes that are economic, simple to use, and do not require well-trained personnel.

Use of microextraction by packed sorbents and gas chromatography-mass spectrometry for the determination of polyamines and related compounds in urine

A novel methodology for the determination of ornithine, putrescine, cadaverine, spermidine and gamma-amino butyric acid in urine samples has been developed. The method uses in situ aqueous derivatization followed by automated microextraction by packed sorbent coupled to a gas chromatography-mass spectrometry system equipped with a programmed temperature vaporizer. This instrumental configuration minimizes sample manipulation due to from the mixing of the reagents, the process is completely automated. The analytes were derivatized using ethyl chloroformate as derivatization reagent. The reaction occurred in aqueous medium and was carried out in 1min in the vial of an autosampler used to perform microextraction by packed sorbent. The parameters affecting derivatization, extraction and separation were optimized in order to obtain maximum sensitivity. Calibration curves were obtained for five calibration levels in three different matrices. All the calibration models displayed good linearity, with R(2) values higher than 0.95. The validity of the models was checked using ANOVA, and it was observed that they did not exhibit any lack of fit. Repeatability and reproducibility was evaluated, with values below 15% in both cases. LOD and LOQ values were found to be in the low μg/L level. Influence of the matrix was confirmed, thus quantification was performed using the standard additions method and normalization to IS. The method developed was applied to the analysis of these compounds in urine samples from healthy individuals and cancer diagnosed patients (Internal Medicine Unit of the Virgen de la Vega Hospital, Salamanca, Spain). Significant differences (Mann-Whitney U test) were observed for putrescine and ornithine concentrations.

A Biginelli-based organic nanoprobe for simultaneous estimation of tyramine and 1,2-diaminopropane: application in real samples

An Ag(i) complex of organic nanoparticles has been developed for the detection of biogenic amines in milk and wine samples.

Silver nanoprism etching-based plasmonic ELISA for the high sensitive detection of prostate-specific antigen

Ultrasensitive and quantitative detection using simple and low-cost assays is critical in clinical diagnostics. In this report, we developed a triangular silver nanoprism (AgNPRs) etching-based plasmonic biosensor for the detection of cancer biomarkers. The triangular AgNPRs-based plasmonic biosensor is an enzyme-linked immunosorbent assay combined with the enzyme-mediated surface plasmon resonance (SPR) of triangular AgNPRs. Triangular AgNPRs uses the immune response of prostate-specific antigen (PSA) to trigger the glucose oxidase (GOx)-catalysed oxidation of glucose (Glu), producing hydrogen peroxide. Hydrogen peroxide acts as an oxidant to etch the triangular AgNPRs into smaller spherical silver nanoparticles, which is accompanied by a substantial blueshift of the SPR peak and a colourimetric blue-to-purple change that can be observed by the naked eye. The SPR peak shift enables the quantitative assessment of PSA due to the remarkable colour change. The triangular AgNPRs-based plasmonic ELISA approach exhibited a quasilinear response to logarithmic PSA concentrations in the range of 10fg/mL to 100pg/mL with a limit of detection (LOD) of 4.1fg/mL. In addition, the LOD of PSA in this approach exceeds that of the conventional HRP-based ELISA (1.25ng/mL) approach by more than 5 orders of magnitude. Patient serum samples from 16 donors were assayed with triangular AgNPRs-based plasmonic ELISA. The results from the triangular AgNPRs-based immunoassay and the time-resolved fluorescence immunoassay showed excellent correlation, and there were no significant differences in the quantified amounts of PSA. The triangular AgNPRs-based plasmonic ELISA approach has advantages (ultrasensitive, cost-effective, ease of operation) that are expected to be of great interest in diagnostics and to be suitable for a point-of-care test.

Spermine detection via metal-mediated ethynylarene 'turn-on' fluorescence signaling

A dicarboxylated ethynylarene was shown to behave as a fluorescent chemosensor for millimolar concentrations of polyamines when mixed with Cd(II), Pb(II) or Zn(II) ions at micromolar concentrations. A bathochromic shift and intensification of fluorescence emission was observed with increasing amounts of metal ion in the presence of aqueous polyamines buffered at pH = 7.6. Such perturbations manifested as 'turn-on' signals from a ratiometric comparison of emission intensities at 390 nm versus 340 nm. Using Pb(II) as the metal mediator, spermine was selectively detected as a 40-fold signal enhancement relative to spermidine, putrescine, cadaverine and several other non-biogenic diamines. Evaluation of additional triamine and tetraamine analytes showed the influence that amine group quantity and spacing had on signal generation. By increasing the ratio of Pb(II) relative to ethynylarene, the detection limit for spermine was successfully lowered to a 25 micromolar level. Noncovalent association between ethynylarene, metal ion and polyamine are believed to promote the observed spectroscopic changes. This study exploits the subtle impact that polyamine structural identity has on transition metal chelation to define a new approach towards polyamine chemosensor development.

A tailor-made nucleoside-based colourimetric probe of formic acid

A ratiometric, specific probe of formic acid has been developed.