Ultrasensitive turn-on fluorescent detection of trace thiocyanate based on fluorescence resonance energy transfer

Gold nanoclusters-based fluorescence resonance energy transfer for rapid and sensitive detection of Pb2

Lead pollution has remained a significant global concern for several decades due to its detrimental effects on the brain, heart, kidneys, lungs, and immune system across all age groups. Addressing the demand for detecting trace amounts of lead in food samples, we have developed a novel biosensor based on fluorescence resonance energy transfer (FRET) from fluorescein R6G to gold nanoclusters (AuNCs-CCY). By utilizing polypeptides as a template, we successfully synthesized AuNCs-CCY with an excitation spectrum that overlaps with the emission spectrum of R6G. Exploiting the fact that Pb2+ induces the aggregation of gold nanoclusters, leading to the separation of R6G from AuNCs-CCY and subsequent fluorescence recovery, we achieved the quantitative detection of Pb2+. Within the concentration range of 0.002-0.20 μM, a linear relationship was observed between the fluorescence enhancement value (F-F0) and Pb2+ concentration, characterized by the linear equation y = 2398.69x + 87.87 (R2 = 0.996). The limit of detection (LOD) for Pb2+ was determined to be 0.00079 μM (3σ/K). The recovery rate ranged from 96 % to 104 %, with a relative standard deviation (RSD) below 10 %. These findings demonstrate the potential application value of our biosensor, which offers a promising approach to address the urgent need for sensitive detection of heavy metal ions, specifically Pb2+, in food samples.

Highly selective detection of deoxyribonucleic acid in living cells using RecA-green fluorescent protein-single-stranded deoxyribonucleic acid filament fluorescence resonance energy transfer probe

A fluorescence resonance energy transfer (FRET) method was developed for double-stranded deoxyribonucleic acid (dsDNA) detection in living cells using the RecA-GFP (green fluorescent protein) fusion protein filament. In brief, the thiol-modified single-stranded DNA (ssDNA) was attached to gold nanoparticles (AuNPs); on the contrary, the prepared RecA-GFP fusion protein interacted with ssDNA. Due to the FRET between AuNPs and RecA-GFP, fluorescence of RecA-GFP fusion protein was quenched. In the presence of homologous dsDNA, homologous recombination occurred to release RecA-GFP fusion protein. Thus, the fluorescence of RecA-GFP was recovered. The dsDNA concentration was detected using fluorescence intensity of RecA-GFP. Under optimal conditions, this method could detect dsDNA activity as low as 0.015 optical density (OD) Escherichia coli cells, with a wide linear range from 0.05 to 0.9 OD cells, and the regression equation was ΔF = 342.7c + 78.9, with a linear relationship coefficient of 0.9920. Therefore, it provided a promising approach for the selective detection of dsDNA in living cells for early clinical diagnosis of genetic diseases.

Amperometric determination of salivary thiocyanate using electrochemically fabricated poly (3, 4-ethylenedioxythiophene)/MXene hybrid film

Thiocyanate (SCN) is a hazardous byproduct of the detoxification of cyanide. Even in minute quantity, the SCN has a negative impact on health. Although there are several ways for SCN analysis, an efficient electrochemical procedure has hardly ever been attempted. Here, the author reports the development of a highly selective and sensitive electrochemical sensor for SCN utilizing Poly (3, 4-Ethylenedioxythiophene) incorporated MXene (PEDOT/MXene) modified screen-printed electrode (SPE). The Raman, X-ray photoelectron (XPS), and X-ray diffraction (XRD) analyses support the effective integration of PEDOT on the MXene surface. Further, scanning electron microscopy (SEM) is employed to demonstrate the formation of MXene and PEDOT/MXene hybrid film. In order to specifically detect SCN in phosphate buffer media (pH 7.4), the PEDOT/MXene hybrid film is grown on the SPE surface via the electrochemical deposition method. Under the optimized condition, the PEDOT/MXene/SPE-based sensor provides a linear response against SCN from 10 to 100 µM and 0.1 μM to 1000 μM with the lowest limit of detections (LOD) of 1.44 μM and 0.0325 μM by differential pulse voltammetry (DPV) and amperometry, respectively. For accurate detection of SCN, our newly created PEDOT/MXene hybrid film-coated SPE demonstrates excellent sensitivity, selectivity, and repeatability. Ultimately, this novel sensor can be used to detect SCN precisely in environmental and biological samples.

Recent advances in nanomaterials-based optical sensors for detection of various biomarkers (inorganic species, organic and biomolecules)

This review briefly emphasizes the different detection approaches (electrochemical sensors, chemiluminescence, surface-enhanced Raman scattering), functional nanostructure materials (quantum dots, metal nanoparticles, metal nanoclusters, magnetic nanomaterials, metal oxide nanoparticles, polymer-based nanomaterials, and carbonaceous nanomaterials) and detection mechanisms. Further, this review emphasis on the integration of functional nanomaterials with optical spectroscopic techniques for the identification of various biomarkers (nucleic acids, glucose, uric acid, oxytocin, dopamine, ascorbic acid, bilirubin, spermine, serotonin, thiocyanate, Pb²⁺ , Cu²⁺ , Hg²⁺ , F^- , peptides, and cancer biomarkers (mucin 1, prostate specific antigen, carcinoembryonic antigen, CA15-3, human epidermal growth factor receptor 2, C-reactive protein, and interleukin-6). Analytical characteristics of nanomaterials-based optical sensors are summarized in Tables, providing the insights of nanomaterials-based optical sensors for biomarkers detection. Finally, the opportunities and challenges of nanomaterials-based optical analytical approaches for the detection of various biomarkers (inorganic, organic, biomolecules, peptides and proteins) are discussed.

Nanozymatic detection of thiocyanate through accelerating the growth of ultra-small gold nanoparticles/graphene quantum dots hybrids

Thiocyanate (SCN^-) concentration monitoring in food is important to ensure the health and safety of the consumers.A colorimetric detection of thiocyanate (SCN^-) based on the nanozymatic activity of gold nanoparticle-graphene quantum dots (GQDs-Au NPs) hybrids in the presence of 3,3',5,5'-tetramethylbenzidine (TMB) and H₂O₂ has been proposed. Here, a new synthesis method of GQDs directly from graphite was introduced. Transmission electron microscopy (TEM) images revealed that the size of the GQDs was 3-5 nm, and the emission peak appeared at 450 nm. As-synthesized GQDs was utilized to produce GQDs-Au NPs hybrids without additional chemicals. However, the presence of SCN^- inhibits the growth of Au NPs, the resulting Au NPs are smaller in size. Moreover, SCN^- group is well-known for hydroxyl radical (OH) scavenging activity that could oxidize TMB. Both effects boosted the nanozymatic activity of GQDs-Au NPs to detect SCN^- under optimized conditions with a limit of detection (LOD) of 3 nM. Present study also validates the methodology to detect SCN^- in raw milk.

Positively Charged Gold Quantum Dots: An Nanozymatic "Off-On" Sensor for Thiocyanate Detection

The concentration of thiocyanate (SCN⁻) in bodily fluids is a good indicator of potential and severe health issues such as nasal bleeding, goiters, vertigo, unconsciousness, several inflammatory diseases, and cystic fibrosis. Herein, a visual SCN⁻ sensing method has been developed using the enzyme-like nature of positively charged gold quantum dots (Au QDs) mixed with 3,3′,5,5′-tetramethylbenzidine (TMB) and hydrogen peroxide (H₂O₂₎. This research also reports a new method of synthesizing positively charged Au QDs directly from gold nanoparticles through a hydrothermal process. Microscopic imaging has showed that the Au QDs were 3–5 nm in size, and the emission wavelength was at 438 nm. Au QDs did not display any enzyme-like nature while mixed up with TMB and H₂O₂. However, the nanozymatic activity of Au QDs appeared when SCN⁻ was included, leading to a very low detection limit (LOD) of 8 nM and 99–105% recovery in complex media. The steady-state kinetic reaction of Au QDs showed that Au QDs had a lower Michaelis–Menten constant (Km) toward H₂O₂ and TMB, which indicates that the Au QDs had a higher affinity for H₂O₂ and TMB than horseradish peroxidase (HRP). A mechanism study has revealed that the scavenging ability of hydroxyl (•OH) radicals by the SCN⁻ group plays an important role in enhancing the sensitivity in this study. The proposed nanozymatic “Off–On” SCN⁻ sensor was also successfully validated in commercial milk samples.

Optical detection of thiocyanate in human saliva based on the colorimetric response of (2-(2-hydroxyphenyl)-1H-benzo[d]imidazol-5-yl)(phenyl) methanone (HBPM)/Co2+ ions conjugate

Simple colorimetric biosensor was designed for the quantification SCN^- ions based on the principle of colorimetric reactions between Co²⁺ and SCN^- ions reaction using synthesized chromophore (2-(2-hydroxyphenyl)-1H-benzo[d]imidazol-5-yl)(phenyl) methanone (HBPM)/Co²⁺ ions conjugate which was synthesized via greener ultrawave sonication method. The structural characterization of the HBPM chromophore was confirmed by using NMR, ESI-MASS spectral techniques and the photophysical properties, sensor studies were done by using UV-Vis Spectrophotometer. Our designed HBPM/Co²⁺ ions conjugates have selectively detected SCN^- ions qualitatively and quantitatively in the presence of other human salivary interferents. As per clinical point of view, three different ranges of SCN^- ions from 0.1 to 2 mM for normal, 3 to 10 mM for disease, and 100-600 µM for below normal ranges were tested successfully by our developed sensor and the LoD was calculated as 5.43 nM. The real potent application of the developed biosensor was tested in human salivary samples of both smokers and non-smokers under different ages and obtained results shown good agreement with existing clinical methods.

How to identify a smoker: a salient crystallographic approach to detect thiocyanate content

There is an increasing demand for monitoring environmental pollutants and the control requires new sensing materials with better sensitivity, selectivity and reliability. In this study, a series of Co₇ clusters incorporating various flexible polyhydroxyamine ligands are explored, with the first report of thiocyanate recognition triggered by crystal formation using a Co₇ crystal (1). For this, we have fortunately synthesized three new mixed metal Co₇ clusters with fascinating structural features. The clusters were characterized by spectroscopic and single crystal X-ray diffraction methods and later by DFT calculations. Due to its better emission spectrum, 1 was further utilized for evaluating its sensing ability towards various anions in water. Surprisingly, 1 shows better quenching ability towards the recognition of SCN⁻ with a better binding constant. The luminescence quenching towards SCN⁻ detection was further verified by the single crystal method, HSAB principle (symbiosis) and theoretical calculations such as DFT studies. The SCXRD data clearly suggest that the Co₇ (1) can be converted into Co₁₄ (1a) by direct reaction with NaSCN under ambient conditions. Besides the soft/hard acid–base concept (symbiosis), the energies of formation, and Co–NCS and Co–OH₂ bond energies (as unravelled by DFT) are responsible for this transformation. Therefore, 1 can be used as a selective and sensitive sensor for the detection of thiocyanate anions based on the fluorescence amplification and quenching method. Further, the designed cluster has also been utilized to detect anions in human blood samples to differentiate a smoker and a non-smoker. It has been concluded that the samples of smokers have a high degree of thiocyanate (∼12 or 9.5 mg L⁻¹) in comparison to those of non-smokers (2–3 mg L⁻¹). Thus, this kind of cluster material has high potentiality in the field of bio-medical science in future endeavours for identification of the extent of thiocyanate content in smokers.

A new Co based sensor for thiocyanate recognition by formation of the dimeric crystals is designed to distinguish a smoker from a non-smoker.

Inhibited oxidase mimetic activity of palladium nanoplates by poisoning the active sites for thiocyanate detection

In this work, a novel convenient colorimetric method for sensitive detection of thiocyanate (SCN^-) has been developed based on its suppression of the oxidase-like activity of palladium square nanoplates on reduced graphene oxide (Pd SP@rGO). SCN^- can be adsorbed onto the surface of Pd SP@rGO via binding with Pd atoms and blocks the active sites that mimic oxidase, thus inhibiting the corresponding chromogenic reaction of 3,3',5,5'-tetramethylbenzidine, which has been comprehensively revealed by the UV-vis spectra and X-ray photoelectron spectra. The color fading exhibits SCN^- concentration-dependent behavior and can be easily recorded by either UV-vis spectroscopy or naked-eye observation. Therefore, both quantitative detection via measurement of the decrease in absorbance and visual detection of SCN^- can be achieved. Owing to the intrinsic amplification of signals by the oxidase-like activity of Pd SP@rGO without resorting to unstable and destructive H₂O₂, this assay is straightforward, robust and sensitive enough for the detection of SCN^- in real samples. Furthermore, an "INH" logic gate is rationally constructed based on the proposed colorimetric SCN^- sensor.

The small silver nanoparticle-assisted homogeneous sensing of thiocyanate ions with an ultra-wide window based on surface-enhanced Raman-extinction spectroscopy

For the first time, we present an original sensing strategy with an ultra-wide detection window from 17 nM to 20 mM to detect SCN- ions. Initially, we investigated the clustering and optical properties of noble metal sol nanoparticles (NPs) due to the competitive interaction of thiocyanate ions (SCN-) and cetyltrimethylammonium bromide (CTAB) under weak acidic conditions, and found that different dimensions and scales of nanoclusters containing the alkyne-embedded Au@Ag NPs and relatively small Ag NPs could be achieved by the mediation of CTAB through electrostatic forces and hydrophobic interaction, in which SCN- could be covalently bonded with the silver surface of NPs to form a compact molecular layer (-Ag-S-C[triple bond, length as m-dash]N), and CTAB could only occupy remaining sites. In this process, we found that SCN- always runs counter to CTAB and tends to dissolve nanoclusters, so that they occupy the exposed surface of NPs in nanoclusters rather than the binding sites of one another. Remarkably, when the concentration of SCN- initially increased, two highly recognizable SERS emissions, which were assigned to alkyne reporter molecules (2208 cm-1) and C[triple bond, length as m-dash]N of SCN- (2110 cm-1), respectively, were rapidly detected, and their ratios (I2110/I2208) increased linearly proportional to the concentration of SCN- over a range of 17 nM to 172 μM, with a limit of detection (LOD) of 10 nM. With the further increase of SCN-, small Ag NPs started to desorb from the surface of individual Au@Ag NPs and dissociated in the solution but did not contribute to SERS signals. Instead, the surface plasmon resonance (SPR) peak of pure silver NPs at 385 nm increased gradually in the range from 0.5 to 20 mM with an LOD of 0.2 mM. Of particular significance, this simple sensor in conjunction with surface-enhanced Raman-extinction spectroscopy can be used for the rapid detection of extensive samples with an ultra-wide detection window, such as body fluids (saliva, urine, and serum) and food (milk powder and brassica vegetables), which is far superior to that of ion chromatography (IC).

3D Microfluidic Devices in a Single Piece of Paper for the Simultaneous Determination of Nitrite and Thiocyanate

The concentrations of nitrite and thiocyanate in saliva can be used as the biomarkers of the progression of periodontitis disease and environmental tobacco smoke exposure, respectively. Therefore, it is particularly necessary to detect these two indicators in saliva. Herein, the three-dimensional single-layered paper-based microfluidic analytical devices (3D sl-μPADs) were, for the first time, fabricated by the spraying technique for the colorimetric detection of nitrite and thiocyanate at the same time. The conditions for 3D sl-μPADs fabrication were optimized in order to well control the penetration depth of the lacquer in a paper substrate. Then, the developed 3D sl-μPADs were utilized to simultaneously detect nitrite and thiocyanate and the limits of detection are 0.0096 and 0.074 mM, respectively. What is more, the μPADs exhibited good specificity, good repeatability, and acceptable recoveries in artificial saliva. Therefore, the developed 3D sl-μPADs show a great potential to determine nitrite and thiocyanate for the assessment of the human health.

Detecting Mercury (II) and Thiocyanate Using "Turn-on" Fluorescence of Graphene Quantum Dots

In this work, 1.8 nm graphene quantum dots (GQDs), exhibiting bright blue fluorescence, were prepared using a bottom-up synthesis from citric acid. The fluorescence of the GQDs could be almost completely quenched (about 96%) by adding Hg²⁺. Quenching was far less efficient with other similar heavy metals, Tl⁺, Pb²⁺ and Bi³⁺. Fluorescence could be near quantitatively restored through the introduction of thiocyanate. This "turn-on" fluorescence can thus be used to detect both or either environmental and physiological contaminants mercury and thiocyanate and could prove useful for the development of simple point-of-care diagnostics in the future. Graphical Abstract.

Core-shell Au@Pt Nanoparticles Catalyzed Luminol Chemiluminescence for Sensitive Detection of Thiocyanate

In this study, core-shell Au@Pt nanoparticles (Au@Pt NPs) with peroxidase catalytic activity were synthesized by the seed-mediated method, and were used to catalyze the reaction of luminol-H₂O₂ to enhance the chemiluminescence (CL) intensity. It was found that thiocyanate (SCN^-) can effectively inhibit the catalytic activity of Au@Pt NPs. Based on this phenomenon, a method to detect SCN^- by using the Au@Pt NPs-catalytic luminol-H₂O₂ CL system was established, which has an ultra-low detection limit and an ultra-wide linear range, as well as the advantages of being simple and having low-cost and convenient operation. The research mechanism indicated that SCN^- could be adsorbed on the surface of Au@Pt NPs and occupies the active sites of Pt nanostructures, which led to a decrease in the amount of Pt⁰ and a loss of the excellent catalytic activity of Au@Pt NPs. After optimizing the experimental conditions, this assay for detecting SCN^- exhibited a good linear range from 5 to 180 nM, and the low detection limit was 2.9 nM. In addition, this approach has been successfully applied to the detection of SCN^- in tap-water samples, which has practical application value and embodies good development prospects.

Nano-fluorescent probes based on DNA-templated copper nanoclusters for fast sensing of thiocyanate

A fast and label-free fluorescent sensor was developed to determine SCN⁻via inhibiting the formation of DNA-templated copper nanoclusters (CuNCs).

Novel fluorescein- and pyridine-conjugated schiff base probes for the recyclable real-time determination of Ce3+ and F. Methods Appl Fluoresc 2019;8:015002. [PMID: 31622961 DOI: 10.1088/2050-6120/ab4ee7]

The effect of aminopyridines substituted at different positions on the fluorescence properties deserves to be studied. Since 2-aminopyridyl-based probes have been reported, the effects of 3-aminopyridine and 4-aminopyridine on the performance of fluorescein probes were discussed in here. Two Schiff base fluorescein probes FN-1, FN-2 were designed and synthesized. Among them, since the ligand shows a highly selective and sensitive response to metal charge transfer (LMCT), the fluorescence of FN-1 can be quenched by Ce³⁺ ions in PBS buffer. At the same time, a specific precipitation reaction between Ce³⁺ and F^- releases the free probe to restore the fluorescence of FN-1. Therefore, FN-1 can be used for the recyclable 'ON-OFF-ON' detection of Ce³⁺and F^-. The detection limits for Ce³⁺and F^- are 4.48 μM and 11.58 μM in concentration range of 0-50 μM and 0-150 μM. However, due to the para position of N and amino groups on 4-aminopyridine, the spatial structure of FN-2 cannot be complexed with ions, resulting in poor selectivity. Polyvinylidene fluoride (PVDF) membrane containing FN-1 were prepared for the real-time qualitative detection of Ce³⁺and F^- in real water samples. FN-1 exhibits high water solubility and biocompatibility and has been successfully applied to biological imaging in vascular smooth muscle cells (VSMCs).

Novel fluorene-based fluorescent probe with excellent stability for selective detection of SCN- and its applications in paper-based sensing and bioimaging

SCN- is one of the most important anions in metabolic processes. However, the investigation of SCN- in living systems is restricted by the lack of stable functional molecular tools. Herein, the first fluorene-based polymer fluorescent probe V1 was synthesized through rational design. Compared with small molecule fluorescent probes, V1 exhibited excellent fluorescence stability in bovine serum albumin (BSA) solution. Furthermore, the V1-based paper sensor was highly selective toward SCN- in aqueous solution. Significantly, these merits of the probe V1 enable the detection of SCN- in different living cell lines and zebrafish.

G-Quadruplex-Based Fluorescent Turn-On Ligands and Aptamers: From Development to Applications

Guanine (G)-quadruplexes (G4s) are unique nucleic acid structures that are formed by stacked G-tetrads in G-rich DNA or RNA sequences. G4s have been reported to play significant roles in various cellular events in both macro- and micro-organisms. The identification and characterization of G4s can help to understand their different biological roles and potential applications in diagnosis and therapy. In addition to biophysical and biochemical methods to interrogate G4 formation, G4 fluorescent turn-on ligands can be used to target and visualize G4 formation both in vitro and in cells. Here, we review several representative classes of G4 fluorescent turn-on ligands in terms of their interaction mechanism and application perspectives. Interestingly, G4 structures are commonly identified in DNA and RNA aptamers against targets that include proteins and small molecules, which can be utilized as G4 tools for diverse applications. We therefore also summarize the recent development of G4-containing aptamers and highlight their applications in biosensing, bioimaging, and therapy. Moreover, we discuss the current challenges and future perspectives of G4 fluorescent turn-on ligands and G4-containing aptamers.

A far-red FRET fluorescent probe for ratiometric detection of l-cysteine based on carbon dots and N-acetyl-l-cysteine-capped gold nanoparticles

A novel far-red fluorescence resonance energy transfer (FRET) fluorescent probe for ratiometric detection of l-cysteine (l-Cys) has been designed. The system was established a FRET assembly by positively charged carbon dots (CDs) and negatively charged N-acetyl-l-cysteine capped gold nanoparticles (NAC-AuNPs). The fluorescence of CDs at 539 nm could be effectively quenched in the presence of NAC-AuNPs owing to FRET process, while the emission of NAC-AuNPs at 630 nm was appeared. Subsequently, the interactions between l-Cys and NAC-AuNPs resulted in the decreased emission intensity of NAC-AuNPs, but the emission intensity of CDs kept almost constant due to the continuous FRET efficiency. The ratio of emission intensities at 539 and 630 nm (I₅₃₉/I₆₃₀) exhibited a linear correlation to the l-Cys concentration in the range of 1.0-110 μM with the detection limit of 0.16 μM. Moreover, this far-red ratiometric sensor also revealed excellent selectivity toward l-Cys over other amino acids, which showed very high potential in the practical application for diagnosing of cysteine-related disease.

Synthesis and spectral analysis of fluorescent probes for Ce4+ and OCl- ions based on fluorescein Schiff base with amino or hydrazine structure: Application in actual water samples and biological imaging

Two Schiff base fluorescein probes (FDA, FDH) based on fluorescein-aldehyde and nitroaniline derivatives were synthesized. The effects of amino and hydrazine substituents in fluorescein backbones were examined via fluorescence and absorbance spectra. In the presence of Ce⁴⁺, the fluorescence of FDA was quenched due to the ligand to metal charge transfer (LMCT). Hypochloric acid can react with the CN bond, and blocking the photo induced electron transfer (PET) of FDH leads to enhancement of the fluorescence. FDA showed detection limits for Ce⁴⁺ and OCl^- as low as 63 nM in concentration range of 0-4 μM. FDH showed detection limits for OCl^- as low as 0.8 μM in concentration rang 0-100 μM. Polyvinylidene fluoride (PVDF) membrane containing the probes was prepared for the real-time qualitative detection of Ce⁴⁺ and OCl^- in real water samples. The probes were successfully applied to biological imaging in vascular smooth muscle cells (VSMCs) and are expected to find applications in biosensing.

Recent progress in nanomaterial-based assay for the detection of phytotoxins in foods

Phytotoxins refers to toxic chemicals derived from plants. They include both secondary metabolites that are dose-dependently toxic and allergens that can cause anaphylactic shock in sensitive individuals. Detecting phytotoxins in foods is increasingly important. Conventional methods for detecting phytotoxins lack sufficient sensitivity and operational convenience. Nanomaterial-based determination assays show great competence in fast and accurate sensing of trace substances. In the present review, representative phytotoxin categories of alkaloids, cyanides, and proteins are discussed. Application of notable nanomaterials, e.g. carbon nanotubes, graphene oxide, magnetic nanoparticles, metal-based nanotools, and quantum dots, in specific sensing strategies to fit the physiochemical properties of the target toxins are summarized. Nanomaterials mainly play four roles in phytotoxin detection: 1) analyte enricher; 2) sensor structure mediator; 3) target recognizer or reactant; 4) signaling agent. Great achievements have been made in the detection of trace plant-derived toxins in food matrices, yet there are still challenges awaiting further investigation.

Diagnosis of Tuberculosis Using Colorimetric Gold Nanoparticles on a Paper-Based Analytical Device

We have developed a colorimetric sensing strategy employing gold nanoparticles and a paper-based analytical platform for the diagnosis of tuberculosis (TB). By utilizing the surface plasmon resonance effect, we were able to monitor changes in the color of a gold nanoparticle colloid based on the effects of single-stranded DNA probe molecules hybridizing with targeted double-stranded TB DNA. The hybridization event changes the surface charge density of the nanoparticles, causing them to aggregate to various degrees, which modifies the color of the solution in a manner that can be readily measured to determine the concentration of the targeted DNA analyte. In order to adapt this TB diagnosis method to resource-limited settings, we extended this label-free oligonucleotide and unmodified gold nanoparticle solution-based technique to a paper-based system that can be measured using a smartphone to obtain rapid parallel colorimetric results with low reagent consumption and without the need for sophisticated analytical equipment. In this study, we investigated various assay conditions, including the denaturing temperature and time, different oligonucleotide probe sequences, as well as the ratio of single stranded probe and double stranded target DNA. After optimizing these variables, we were able to achieve a detection limit of 1.95 × 10^-2 ng/mL for TB DNA. Furthermore, multiple tests could be performed simultaneously with a 60 min turnaround time.

Hydride generation-resonance Rayleigh scattering and SERS spectral determination of trace Bi

In acidic solutions, Bi(III) was reduced by NaBH4 to form BiH3 gas. Using I3(-)graphene oxide (GO) as absorption solution, the BiH3 gas reacted with I3(-) to form I(-) that resulted in the I3(-) concentration decreasing. In the absence of BiH3, the I3(-) concentration was high, and as receptors it was closed to the surfaces of GO which was as donors. Then the surface plasmon resonance Rayleigh scattering (RRS) energy of GO transfers to I3(-) heavily, and results in the RRS quenching severely. With the increase of the Bi(III) concentration, the receptors and the RRS energy transfer (RRS-ET) decreased, so the RRS intensity enhanced linearly at 370nm. The RRS intensity was linear to the Bi(III) concentration in 0.05-5.5μmol/L, with a detection limit of 4ng/mL Bi. A new RRS-ET spectral method was developed for the determination of trace Bi(III). Using I3(-) as the absorption solution, silver nanorod (AgNR) as sol substrate and Vitoria blue B (VBB) as molecular probe, a SERS method was developed for detection of Bi.

Interaction of the ginsenosides with κ-casein and their effects on amyloid fibril formation by the protein: Multi-spectroscopic approaches

The interaction of the ginsenosides (GS) including ginsenoside Rg1, Rb1 and Re with κ-casein and the effects of GS inhibiting amyloid fibril formation by κ-casein have been investigated in vitro by fluorescence and ultraviolet spectra. Results showed that Rg1 and Rb1 had dose-dependent inhibitory effects on reduced and carboxymethylated κ-casein (RCMκ-CN) fibril formation, while Re resulted in an increase in the rate of fibril formation. The enhancement in RLS intensity was attributed to the formation of new complex between GS and RCMκ-CN, and the corresponding thermodynamic parameters (ΔH, ΔS and ΔG) were assayed. The steady-state ultraviolet-visible absorption spectra had also been tested to observe if the ground-state complex formed, and it showed the same result as RLS spectra. The binding constants and the number of binding sites between GS and RCMκ-CN at different temperatures had been evaluated from relevant fluorescence data. According to the Förster non-radiation energy transfer theory, the binding distance between RCMκ-CN and GS was calculated. The fluorescence lifetime of RCMκ-CN was longer in the presence of GS than in absence of GS, which was evident that the hydrophobic interaction plays a major role in the binding of GS to RCMκ-CN. From the results of synchronous fluorescence, it could be deduced that the polarity around RCMκ-CN Trp97 residue decreased and the hydrophobicity increased after addition of Rg1 or Rb1. Based on all the above results, it is explained that Rg1 and Rb1 inhibited amyloid fibril formation by κ-casein because the molecular spatial conformation and physical property of κ-casein changed causing by the complex formation between GS and κ-casein.

Paper-based analytical device for instrumental-free detection of thiocyanate in saliva as a biomarker of tobacco smoke exposure

This work describes a fast and simple assay for in situ detection of thiocyanate, i.e., a biomarker of tobacco smoke exposure, in human saliva. The assay is based on the formation of an iron(III)-thiocyanate colored complex in a paper-based sensing platform and subsequent image analysis using a scanner as detection device. Experimental parameters influencing the color intensity of the complex were fully evaluated, including the selection of detection conditions, type of paper substrate, test zone dimensions and composition as well as the stability of the paper-based device. Under optimal conditions, the detection limit was 0.06mM of thiocyanate, and the repeatability, expressed as relative standard deviation, was 3%. The proposed method, characterized by its simplicity, portability and low sample consumption, was applied to the detection of thiocyanate in a series of human saliva samples. Average thiocyanate levels in the ranges 0.28-0.87mM and 0.78-4.28mM were found for non-smokers and smokers, respectively. Recovery studies were carried out at two concentration levels, showing recovery values in the range of 96.1-103.6%.

A dual-mode signaling response of a AuNP-fluorescein based probe for specific detection of thiourea

By employing fluorescein and AuNPs as energy donors and acceptors, respectively, a novel fluorescence resonance energy transfer (FRET)-based dual-mode sensor for selective recognition and quantitative detection of thiourea was designed and constructed in this study for the first time.

Sensitive detection of cyanide using bovine serum albumin-stabilized cerium/gold nanoclusters

A simple, sensitive, and selective fluorescence assay for the detection of CN(-) has been demonstrated using bovine serum albumin-stabilized cerium/gold nanoclusters (BSA-Ce/Au NCs). When excited at 325 nm, BSA-Ce/Au NCs have two fluorescence bands centered at 410 and 658 nm, which are assigned to BSA-Ce/Au complexes and Au NCs, respectively. Each BSA-Ce/Au NC contains 22 Au atoms and 8 Ce ions. Through etching of the Au core in BSA-Ce/Au NCs by CN(-), the fluorescence at 658 nm is quenched, while that at 410 nm enhances during the formation of complexes among BSA, Ce(4+), and [Au(CN)2](-). The circular dichroism spectra reveal that relative to BSA-Au NCs, BSA-Ce/Au NCs have looser structures of the BSA templates. As a result, it is easier for CN(-) to access the Au cores in BSA-Ce/Au NCs, allowing faster (within 15 min) etching of the Au cores by CN(-). At pH 12.0, this assay allows the detection of CN(-) down to 50 nM, with linearity over 0.1-15 μM. This assay has been applied to the determination of the concentrations of CN(-) in spiked drinking water and pond water samples.

A dual-mode colorimetric and fluorometric “light on” sensor for thiocyanate based on fluorescent carbon dots and unmodified gold nanoparticles

A novel, highly sensitive and selective dual-readout (colorimetric and fluorometric) sensor based on fluorescent carbon dots (CDs) and unmodified gold nanoparticles (AuNPs) for the detection of thiocyanate (SCN⁻) was proposed.

Detection of thiocyanate through limiting growth of AuNPs with C-dots acting as reductant

We have found that hydroxyl-rich carbon dots (C-dots) have the ability to reduce Au³⁺to form gold nanoparticles (AuNPs) which can be used as an optical sensor to detect SCN⁻in raw milk with satisfactory results.