An electrochemiluminescent (ECL) aptamer based method is described for the determination of thrombin. Three-dimensional nitrogen-doped graphene oxide (3D-NGO) was placed on a glassy carbon electrode (GCE) to provide an electrode surface that displays excellent electrical conductivity and acts as a strong emitter of ECL. The modified electrode was further coated with chitosan via electrodeposition. Finally, the amino-modified aptamer was immobilized on the modified GCE. The interaction between thrombin and aptamer results in a decrease in ECL. The assay has a linear response in the 1 fM to 1 nM thrombin concentration range and a 0.25 fM lower detection limit (at an S/N ratio of 3). The method was applied to the determination of thrombin in spiked human plasma samples, and recoveries ranged between 94 and 105% (with RSDs of <3.6%). The calibration plot was recorded at potential and wavelength of fluorescence emission (wavelength:?445 nm; potential:?0 to -2 V).
Graphical abstract A bare glassy carbon electrode (GCE) does not display electrochemiluminescence (ECL). If, however, nitrogen-doped graphene quantum dots, chitosan, and three-dimensional nitrogen-doped graphene oxide (NGQD-chitosan/3D-NGO) are electrodeposited on the GCE, strong ECL can be observed. The ECL intensity decreased after aptamer and bovine serum albumin (BSA) were dropped onto the electrode (curve a). However, the ECL further decreases after addition of thrombin (TB; curve b).
The electrogenerated chemiluminescence (ECL) of methionine stabilized gold nanoclusters (Met-AuNCs) is presented. The Met-AuNCs were used to modify a glassy carbon electrode (Met-AuNC/GCE) which is shown to exhibit a stable and strong cathodic ECL signal (at ?1.86 V) when using potassium peroxodisulfate (K2S2O8) as the coreactant in aqueous solution of pH 7.4. Compared to a GCE modified with BSA-AuNCs, the ECL intensity of Met-AuNCs is 5-fold enhanced. The possible ECL reaction mechanism of the ECL system was studied, and a method for the determination of dopamine (DA) was worked out. The modified GCE has a linear response in the 0.1 to 4 μM DA concentration range, with a detection limit of 32 nM (at an S/N ratio of 3). The method was applied to the determination of DA released by PC12 cells. In our perception, the Met-AuNC/GCE provides a viable new tool in ECL based bioanalysis that also paves new routes to the design and application of new sensors.
Graphical abstract The electrochemiluminescence (ECL) sensor based on methionine stabilized gold nanocluster modified glassy carbon electrode (Met-AuNC/GCE) using potassium peroxodisulfate (K2S2O8) as the coreactant in aqueous solution was fabricated for the highly sensitive detection of dopamine (DA) released by cells.
The authors describe an electrochemiluminescence (ECL) based aptasensor for the pesticide aldicarb. The method is based on effective ECL energy transfer that occurs between the ruthenium(II) bipyridyl complex [referred to as Ru(bpy)32+] and gold nanoparticles (AuNPs). More specifically, multiwalled carbon nanotubes were modified with dendritic poly(L-arginine) labeled with Ru(bpy)32+, and the aptamers were taggedd with AuNPs. In the absence of aldicarb, the ECL emitted by Ru(bpy)32+ is enhanced by AuNPs under peak wavelength at at a wavelength of 610 nm. In the presence of aldicarb, the capture and competitive binding of aldicarb to the DNA aptamers causes their separation from the DPA6/Ru(bpy)32+/MWCNT. As a result, ECL intensity decreases linearly with increasing aldicarb concentrations in the range between 40 pM and 4 nM, with a detection limit of 9.6 pM. This aptamer switch is highly sensitive, selective and inexpensive. Conceivably, it can be adapted to formats for the determination of other pesticide residues by using different DNA aptamers.
Graphical abstract Schematic of the procedure for aptamer-based detection of aldicarb using the ECL signal of the Ru(bpy)32+ amplified by gold nanoparticles. This assay has high sensitivity, good selectivity, and low cost. It can presumably be transferred to other pesticide detection schemes.
CdSe:Eu nanocrystals were successfully synthesized and characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectric spectroscopy. The CdSe:Eu nanocrystals showed enhanced green electrochemiluminescence (ECL) intensity when compared to pure CdSe nanocrystals. Further, the nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen (CEA) that has a linear response over the 1.0 fg·mL?1 to 100 ng·mL?1 CEA concentration range with a 0.4 fg·mL?1 detection limit. The assay was applied to the determination of CEA in human serum samples.
Graphical abstract Schematic of the assay: GCE-glassy-carbon electrode, Ab- Antibody, BSA- Bovine serum albumin, Ag- Antigen. CdSe:Eu nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen.
Carbon nanodots modified with triethylenetetramine (referred to as TCDs) are shown to be viable fluorescent probes for relay recognition of Cu(II) ion and glutathione (GSH). The assay is based on an “on-off-on” mechanism where the “on-off” effect, i.e. quenching by Cu(II) by up to 67%, is exploited to quantify it in concentrations as low as 3.4 nM. The unique quenching of fluorescence (measured at excitation/emission wavelengths of 380/470 nm; quantum yield 16%) is attributed to the fairly selective capture of Cu(II) by the amino and amide groups on the surface of the TCDs. On addition of GSH to the quenched TCD/Cu(II) complex, fluorescence is restored. This effect enables GSH to be quantified in the 0.2 to 175 μM concentration range, with a 0.11 μM detection limit. The turn-on response to GSH is highly selective over other natural amino acids and common anions. Furthermore, the TCDs were successfully applied to image Cu(II) and GSH in living yeast cells.
Graphical Abstract Carbon nanodots modified with triethylenetetramine show strong blue fluorescence which is quenched by Cu(II) but restored on addition of glutathione. Both Cu(II) (down to 3.4 nM) and glutathione (down to 110 nM) can be detected via these effects.
The authors describe an electrochemiluminescence (ECL) assay for the determination of 2,4,6-trinitrotoluene (TNT) in soil. It is based on the finding that graphene quantum dots (GQDs) strongly enhance the ECL of CdSe quantum dots (CdSe QDs), and ECL is strongly quenched by TNT. In order to assemble the GQDs and CdSe QDs, the latter were functionalized with carboxy groups and then coupled to amino-functionalized GQDs (afGQDs). The resulting CdSe-GQDs conjugation was placed as a thin film on a glassy carbon electrode (GCE). The modified electrode displays an about 8-fold enhanced ECL intensity compared to an GCE with CdSe QDs only, and the onset potential of the ECL reaction is positively shifted by 140 mV. In the presence of TNT, the ECL is quenched due to the formation of the TNT-amine complex. The decrease in ECL intensity is related to the logarithm of the TNT concentration in the range from 0.01 to 100 ppb, with a detection limit as low as 3 ppt. The results of TNT assays in (spiked) soil samples showed recoveries between 99.2 and 105.0 % and relative standard deviations between 3.0 and 8.2 %. This strategy offers a new perspective for developing ECL assays based on the use of semiconductor nanoparticles and graphene-based nanomaterials.
Graphical abstract A electrochemiluminescence (ECL) assay was developed for the detection of 2,4,6-trinitrotoluene (TNT). The method utilizes a combination of CdSe and graphene quantum dots (GQDs), and a glassy carbon electrode modified with poly(diallyldimethylammonium chloride)-protected graphene. The assay is simple and displays acceptable reproducibility.
The authors described gold nanoclusters (AuNCs) for use on an “on ? off ? on” NIR fluorescent probe for the determination of citrate and Cu(II) ion. The AuNCs were prepared by a microwave-assisted method using BSA as both the stabilizing and reducing agent. The resulting BSA-capped AuNCs display NIR fluorescence peaking at 680 nm under 500 nm excitation, a quantum yield of ~6.0%, an average size of 2.8 ± 0.5 nm, water-dispersibility, stability and biocompatibility. The on?off probe for Cu(II) is based on the interaction between Cu(II) and BSA which causes the fluorescence of the BSA?AuNCs to be quenched. The quenched fluorescence is recovered on addition of vitamin C (VC), obviously due to complexation of Cu(II) by citrate. The probe was employed to image Cu(II) and citrate in HeLa cells and in aqueous solutions. The method works in the 20 nM to 0.1 mM concentration range for Cu(II), and in the 8 nM to 120 μM concentration range for VC.
Graphical abstract Schematic presentation of the gold nanocluster based probe whose fluorescence is quenched by Cu(II) ions and then restored by addition of vitamin C. This is demonstrated for both aqueous solutions and living cells.
Various carbon nanomaterials for use in anodic stripping voltammetric analysis of Hg(II), Cu(II), Pb(II) and Cd(II) are screened. Graphene, carbon nanotubes, carbon nanofibers and fullerene (C60), dispersed in chitosan (Chit) aqueous solution, are used to modify a glassy carbon electrode (GCE). The fullerene-chitosan modified GCE (C60-Chit/GCE) displays superior performance in terms of simultaneous determination of the above ions. The electrodes and materials are characterized by electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The excellent performance of C60-Chit/GCE is attributed to the good electrical conductivity, large surface area, strong adsorption affinity and unique crystalline structure of C60. Using differential pulse anodic stripping voltammetry, the assay has the following features for Hg(II), Cu(II), Pb(II) and Cd(II), respectively: (a) Peak voltages of +0.14, ?0.11, ?0.58 and???0.82 V (vs SCE); (b) linear ranges extending from 0.01–6.0 μM, 0.05–6.0 μM, 0.005–6.0 μM and 0.5–9.0 μM; and (c), detection limits (3σ method) of 3 nM (0.6 ppb), 14 nM (0.9 ppb), 1 nM (0.2 ppb) and 21 nM (2.4 ppb). Moreover, the modified GCE is well reproducible and suitable for long-term usage. The method was successfully applied to the simultaneous determination of these ions in spiked foodstuff.
Graphical abstract Compared with graphene, carbon nanotubes and carbon nanofibers, an electrode modified with fullerene in chitosan electrode displays superior performance for the simultaneous anodic stripping voltammetric detection of Hg(II), Cu(II), Pb(II) and Cd(II).
The authors report on a one-pot approach for synthesizing highly fluorescent protamine-stabilized gold nanoclusters. These are shown to be a viable nanoprobe for selective and sensitive fluorometric determination of lead(II) via quenching of fluorescence via Pb(II)-Au(I) interaction. Under optimized conditions, fluorescence measured at excitation/emission peaks of 300/599 nm drops in the 80 nM–15 μM lead(II) concentration range. The detection limit is 24 nM, and relative standard deviations (for n?=?11) at concentrations of 0.10, 4.0 and 15 μM are 1.6, 2.5 and 1.9%, respectively. The relative recoveries of added lead(II) in the water samples ranged from 97.9?±?2.29% to 101.2?±?1.83%.
Graphical abstract Lead(II) ions are found to be able to selectively and sensitively quench the fluorescence of the protamine-gold nanoclusters (PRT-AuNCs). Thereby, an inexpensive, selective and sensitive lead(II) assay was established.
The authors report that the peroxidase-like activity of Au@Pt core-shell nanohybrids (Au@PtNHs) is selectively inhibited by cysteine. This finding has led to a highly sensitive colorimetric assay for cysteine that is based on the nanohybrid-catalyzed oxidation of TMB by H2O2 to form a blue product. The method has a detection limit of 5.0 nM and a linear range from 10 nM to 20 μM. The assay is highly selective over other amino acids. It was successfully applied to the determination of cysteine in an injection containing a mixture of amino acids.
Graphical abstract The peroxidase-like activity of Au@Pt core-shell nanohybrids (Au@PtNHs) is selectively inhibited by cysteine, enabling the determination of cysteine.
A time-resolved phosphorescence (TRP) is applied to the highly sensitive determination of Fe(II) ions. The method is based on the use of a phosphorescent probe consisting of cysteine-bridged Mn-doped ZnS quantum dots (Mn/ZnS QDs). The presence of cysteine enhances the phosphorescence of the QDs and also increases the efficiency of quenching caused by Fe(II) ions. This results in strongly improved selectivity for Fe(II). The linear response is obtained in the concentration range of 50–1000 nM with a 19 nM detection limit. Phosphorescence is recorded at excitation/emission peaks of 301/602 nm. The interference of short-lived fluorescent and scattering background from the biological fluids is eliminated by using the TRP mode with a delay time of 200 μs. The determination of Fe(II) in human serum samples spiked at a 150 nM level gave a 92.4% recovery when using the TRP mode, but only 52.4% when using steady-state phosphorescence. This demonstrates that this probe along with TRP detection enables highly sensitive and accurate determination of Fe(II) in serum.
Graphical abstract Schematic of a novel phosphorescent method for the detection of Fe2+ ions based on cysteine-bridged Mn-doped ZnS quantum dots. The sensitivity of this assay greatly increases due to the addition of cysteine. Interferences by short-lived auto-fluorescence and the scattering light from the biological fluids is eliminated by using time-resolved phosphorescence mode.
A novel electrochemiluminescent (ECL) method for highly sensitive detection of gene mutations was designed based on the amplification strategy of dual-functional aluminum(III). A film composed of nafion and polyaniline (Nafion-PANI) was placed onto glassy carbon electrode (GCE) in order to improve conductivity and stability, and then cadmium sulfide quantum dots (CdS QDs) were attached as an ECL label. Al(III) was introduced in order to enhance the ECL signal intensity of the CdS QDs by filling the surface electronic defects of CdS QDs. The Al(III) ions also assist by improving sensitivity by promoting the electron transfer at the GCE and by retaining plenty of single-stranded DNA (ssDNA). The ECL is generated at typically ?1.5 V in the presence of containing K2S2O8. Compared to conventional ECL based DNA biosensors, the one described here – based on the use of dually functional Al(III) ions – enables ssDNA to be detected in the 1 f. to 10 nM concentration range, with a 6 f. detection limit. This method was applied to the quantitation of target ssDNA with different mismatching status in human serum. In our perception, it represents a highly attractive tool for the detection of ssDNA and has a particular potential in the diagnosis of hereditary diseases.
Graphical abstract Preparation and schematic illustration of dual-functional aluminum(III)-based electrochemiluminescent for detection of target ssDNA.
The authors report that carbon nitride quantum dots (CN QDs) exert a strong enhancing effect on the Cu(II)/H2O2 chemiluminescent system. Chemiluminescence (CL) intensity is enhanced by CN QDs by a factor of ~75, while other carbon nanomaterials have a much weaker effect. The possible mechanism of the effect was evaluated by recording fluorescence and CL spectra and by examining the effect of various radical scavengers. Emitting species was found to be excited-state CN QDs that produce green CL peaking at 515 nm. The new CL system was applied to the sensitive detection of H2O2 and glucose (via glucose oxidase-catalyzed formation of H2O2) with detection limits (3σ) of 10 nM for H2O2 and 100 nM for glucose. The probe was employed for glucose determination in human plasma samples with satisfactory results.
Graphical abstract The effect of carbon nitride quantum dots (CN QDs) on Cu(II)-H2O2 chemiluminescence reaction was studied and the new CL system was applied for sensitive detection of glucose based on the glucose oxidase (GOx)-catalyzed formation of H2O2.
Gold nanoclusters (AuNCs) protected with a bovine serum albumin (BSA) coating are known to emit red fluorescence (peaking at 650 nm) on photoexcitation with ultraviolet light (365 nm). On addition of Cu(II) ions, fluorescence is quenched because Cu(II) complexes certain amino acid units in the BSA chain. Fluorescence is, however, restored if pyrophosphate (PPi) is added because it will chelate Cu(II) and remove it from the BSA coating on the AuNCs. Because PPi is involved in the function of telomerase, the BSA@AuNCs loaded with Cu(II) can act as a fluorescent probe for determination of the activity of telomerase. A fluorescent assay was worked out for telomerase that is highly sensitive and has a wide linear range (10 nU to 10 fM per mL). The fluorescent probe was applied to the determination of telomerase activity in cervix carcinoma cells via imaging. It is shown that tumor cells can be well distinguished from normal cells by monitoring the differences in intracellular telomerase activity.
Graphical abstract Gold nanoclusters (AuNCs) protected by bovine serum albumin (BSA) and displaying red photoluminescence were prepared as fluorescent probe for the determination of telomerase activity and used for imaging of cervix carcinoma (HeLa) cells.
This review (with 121 references) gives a summary on recent advances in the use of nanomaterials for the optical determination of dopamine. It includes a brief overview of the clinical significance of dopamine followed by a discussion on the recent advances in various nanomaterial-based distinctive optical spectroscopic methods such as (a) colorimetry and spectrophotometry, (b) surface-enhanced Raman spectroscopy (SERS), (c) fluorescence spectrometry, and (d) electrochemiluminescence (ECL) spectrometry. All sections are further divided into subsections based on the type of nanomaterial used, and their advantages and disadvantages are discussed. A discussion on the validity of the nanomaterial-based optical detection of dopamine for human samples is also included. This review concludes with highlights of current challenges of nanomaterial-based optical sensors and an outlook on future perspectives.
Graphical abstract Schematic of the use of various nanomaterials in the detection of dopamine based on colorimetry, spectrophotometry, surface-enhanced Raman spectroscopy, fluorescence and electrochemiluminescence.
The authors report on a disposable sensor for the differential pulse anodic stripping voltammetric (DPASV) determination of the ions Zn(II), Pb(II) and Cu(II). Simultaneous detection is accomplished by using a screen-printed carbon electrode (SPCE) co-modified with an in-situ plated bismuth (Bi)) film and gold nanoparticles (AuNPs). The synergistic effect of the Bi film, and the large surface and good electrical conductivity of the AuNPs strongly assist in the co-deposition of the three ions. Four well-defined and fully separated anodic stripping peaks, at 540 mV for Zn(II), 50 mV for Pb(II), 140 mV for Bi(III) and 295 mV for Cu(II), all vs. Ag/AgCl, can be seen. The modified SPCE was characterized by scanning electron microscopy, X-ray diffraction, cyclic voltammetry and electrochemical impedance spectroscopy. Under the optimized conditions, the sensor has a good response to these ions. The detection limits (at an S/N ratio of 3) are 50 ng·L?1 for Zn(II), 20 ng·L?1 for Pb(II), and 30 ng·L?1 for Cu(II). The method was applied to the determination of the 3 ions in spiked lake water samples.
Graphical abstract Schematic of screen-printed carbon electrode (SPCE) co-modified with a bismuth film and gold nanoparticles for electrochemical simultaneous determination of Zn(II), Pb(II) and Cu(II) by differential pulse anodic stripping voltammetric (DPASV).
Three-dimensional structures comprising polypyrrole nanowires (PPyNWs) and molecularly imprinted polymer (MIP) were prepared by electropolymerization on the surfaces of a glassy carbon electrode (GCE). The modified GCE possesses both large surface area and good electrocatalytic activity for oxidizing dopamine (DA), and this leads to high sensitivity. The electropolymerized MIP has a large number of accessible surface imprints, and this makes the GCE more selective. Under optimal conditions and at a working voltage of typically 0.23 V (vs. SCE), the calibration plot is linear in the 50 nM to 100 μM DA concentration range, and the limit of detection is 33 nM. The sensor has been successfully applied to the analysis of DA in injections.
Graphical abstract Schematic of a three-dimensional nanocomposite based dopamine sensing platform based on the use of a molecularly imprinted polymer and poly(pyrrole) nanowires. The modified polypyrrole nanowires and molecularly imprinted polymer endowed high electrocatalytic capacity and good selectivity for dopamine recognition, respectively.
The authors describe double-shell magnetic nanoparticles functionalized with 2-mercaptobenzothiazole (MBT) to give nanospheres of the type MBT-Fe3O4@SiO2@C). These are shown to be viable and acid-resistant adsorbents for magnetic separation of the heavy metal ions Ni(II), Cu(II) and Pb(II). MBT act as a binding reagent, and the carbon shell and the silica shell protect the magnetic core. Following 12 min incubation, the loaded nanospheres are magnetically separated, the ions are eluted with 2 M nitric acid and then determined by inductively coupled plasma-mass spectroscopy. The limits of detection of this method are 2, 82 and 103 ng L￣1 for Ni(II), Cu(II), and Pb(II) ions, respectively, and the relative standard deviations (for n = 7) are 6, 7.8, and 7.4 %. The protocol is successfully applied to the quantitation of these ions in tap water and food samples (mint, cabbage, potato, peas). Recoveries from spiked water samples ranged from 97 to 100 %.
Graphical abstract Mercaptobenzothiazole-functionalized magnetic carbon nanospheres of type Fe3O4@SiO2@C were synthesized. Then applied for magnetic solid phase extraction of Ni(II), Cu(II) and Pb(II) from water and food samples with LOD of 0.002, 0.082 and 0.103 μg L?1 respectively.
It is shown that triangular silver nanoplates (TAgNPs) are viable colorimetric probes for the fast, sensitive and selective detection of Hg(II). Detection is accomplished by reducing Hg(II) ions to elemental Hg so that an Ag/Hg amalgam is formed on the surface of the TAgNPs. This leads to the inhibition of the etching TAgNPs by chloride ions. Correspondingly, a distinct color transition can be observed that goes from yellow to brown, purple, and blue. The color alterations extracted from the red, green, and blue part of digital (RGB) images can be applied to the determination of Hg(II). The relationship between the Euclidean distances (EDs), i.e. the square roots of the sums of the squares of the ΔRGB values, vary in the 5 nM to 100 nM Hg(II) concentration range, and the limit of detection is as low as 0.35 nM. The color changes also allow for a visual estimation of the concentrations of Hg(II). The method is simple in that it only requires a digital camera for data acquisition and a Photoshop software for extracting RGB variations and data processing.
Graphical abstract Hg2+ detection was achieved by anti-etching of TAgNPs caused by the formation of silver amalgam, along with vivid multicolor variations from yellow to brown, purple, and eventually to be blue.
The authors describe a colorimetric method for the determination of DNA based on the deaggregation of gold nanoparticles (AuNPs) induced by exonuclease III (Exo III). DNA amplification is accomplished by Exo III to generate large quantities of the residual DNA. Residual DNA tethers onto the surfaces of AuNPs which prevents their aggregation. Hence, the color of the solution is red. However, in the absence of DNA, salt-induced aggregation is not prevented, and the bluish-purple color of the aggregated AuNPs is observed. The ratio of absorbances at 525 and 625 nm increases up to 150 nM DNA concentrations, and the LOD is as low as 3.0 nM. It is shown that the presence of 300 nM concentrations of random DNA (with a mass up to 10-fold that of target DNA) does not interfere. The method was successfully applied to the analysis of DNA in spiked serum samples. The method is simple, reliable, and does not require complicated amplification steps and expensive instrumentation.
Graphical abstract Schematic of a sensing strategy for DNA detection by exonuclease III-induced deaggregation of gold nanoparticles. DNA concentrations as low as 3 nM can be detected via colorimetric monitoring of the color change from red to purple-blue.
