Sensitive, Signal-Modulation Strategy for Discrimination of ECL Spectra and Investigation of Mutual Interactions of Emitters.

The intensity of electrochemiluminescence (ECL) usually changes rapidly with the progress of the electrochemical process, making it difficult to determine the ECL spectrum with a conventional photomultiplier in a wavelength scan model. Herein, a band-pass filter (BPF)-involved modulating strategy is proposed to upgrade a conventional ECL analyzer to a highly sensitive ECL spectrometer without changing its hardware. The ECL spectrum can be figured out by rapidly and/or continuously modulating a part of the ECL intensity-time curve with a BPF array of different central wavelengths as well as correcting the ECL intensity at different measurement times by a univariate cubic polynomial model. This strategy not only can determine the spectrum of ultra-weak emission with high sensitivity via merely modulating the emission within a short period, including the weak self-ECL from either Ru(bpy)32+ or tripropylamine (TPA), but also can demonstrate the interaction between the co-existing emitters. It is shown that the ECL from both Ru(bpy)32+ and TPA of the Ru(bpy)32+/TPA system can be mutually promoted in electrochemical potential and in a concentration-dependent way. The self-ECL of TPA at the potential of 1.24 V can be enhanced from 4.9- to 51-fold with the Ru(bpy)32+ concentration increasing from 0.01 to 0.8 µM. In the presence of 0.04 µM Ru(bpy)32+, the self-ECL of TPA is enhanced by 94- and 10.2-fold at the potential of 1.01 and 1.76 V, respectively. The portable inexpensive BPF turntable device is also useful in spectrum-resolved multi-analyte determination and ratiometric ECL biosensors.

Highly Sensitive and Reliable Internal-Standard Surface-Enhanced Raman Scattering Microneedles for Determination of Bacterial Metabolites as Infection Biomarkers in Skin Interstitial Fluid.

Microneedles (MNs) are currently one of the most promising tools for skin interstitial fluid (ISF)-based biosensing, while it is still a challenge to expand the detectable biomarkers in ISF due to limited MNs types and detection techniques. Herein, highly sensitive internal-standard surface-enhanced Raman scattering microneedles (IS-SERS-MNs) were developed, which enabled the reliable detection of bacterial metabolites in ISF as new detectable biomarkers for infection diagnosis. The developed IS-SERS-MNs can not only directly detect pyocyanin (a representative bacterial metabolite) present in mouse dermal ISF but also indirectly detect pyocyanin in the hypodermis via its diffusion into the dermis, revealing a new possible pathway for the source of biomarkers in dermal ISF. Moreover, the SERS signal of pyocyanin was also clearly detected at real mouse wounds, indicating that the developed IS-SERS-MNs have great potential in minimally invasive and painless diagnosis of bacterial infection via a new ISF route. This work not only develops IS-SERS-MNs as a powerful tool for expanding the application of SERS-based MNs but also provides a new chance for ISF-related infection diagnosis.

Near-Infrared Light-Responsive SERS Tags Enable Positioning and Monitoring of the Drug Release of Photothermal Nanomedicines In Vivo.

Understanding the in vivo behavior of photothermal nanomedicines (PTNMs) is important for drug development and evaluation. However, it is still very challenging. Herein, two key parameters, i.e., the depth of PTNMs under biological tissue and the drug release ratio of PTNMs in vivo, can be revealed by a near-infrared (NIR) light-responsive surface-enhanced Raman scattering (SERS) strategy. The fabricated PTNMs were composed of waxberry-like gold nanoparticles, model drug curcumin, and an elaborately selected NIR light-responsive Raman reporter (3,3'-diethylthiatricarbocyanine iodide, DTTC). The response mechanism of DTTC to NIR light was investigated as photodegradation. NIR light irradiation heated the gold nanoparticles, triggered the release of a model drug, and simultaneously decreased the SERS intensity of the PTNMs. In vitro experiment results revealed that the SERS intensity decrease could well reflect the depth of PTNMs with a correlation coefficient of more than 0.99. On this basis, after in situ SERS detection, the depth of PTNMs in a tumor could be revealed with satisfactory accuracy. Moreover, the decrease in the SERS intensity of PTNMs showed a highly similar trend to the increase in the drug release, suggesting that it could be used for real-time monitoring of drug release of PTNMs. This study not only opens a new avenue for the release study of many inactive fluorescent and Raman drugs of PTNMs but also provides an effective way for reporting the depth, which greatly promotes the application of PTNMs in vivo.

Label-Free and Template-Free Chemiluminescent Biosensor for Sensitive Detection of 5-Hydroxymethylcytosine in Genomic DNA.

5-Hydroxymethylcytosine (5hmC) is a modified base present at low levels in various mammalian cells, and it plays essential roles in gene expression, DNA demethylation, and genomic reprogramming. Herein, we develop a label-free and template-free chemiluminescent biosensor for sensitive detection of 5hmC in genomic DNAs based on 5hmC-specific glucosylation, periodate (IO4+) oxidation, biotinylation, and terminal deoxynucleotidyl transferase (TdT)-assisted isothermal amplification strategy, which we term hmC-GLIB-IAS. This hmC-GLIB-IAS exhibits distinct advantages of bisulfite-free, improved sensitivity, and genome-wide analysis of 5hmC at constant reaction temperature without the involvement of either specially labeled nucleic acid probes or specific templates for signal amplification. This method can sensitively detect 5hmC with a detection limit of 2.07 × 10-13 M, and it can detect 5hmC in the whole genome DNA with a detection limit of 3.92 × 10-5 ng/µL. Moreover, this method can distinguish 5hmC from 5-methylcytosine (5mC) and cytosine (C) and even discriminate 0.1% 5hmC in the mixture of 5hmC-DNA and 5mC-DNA. Importantly, this hmC-GLIB-IAS strategy enables genome-wide analysis without the involvement of either isotope-labeled substrates or specific antibodies, providing a powerful platform to detect 5hmC in real genomic DNA with high reproducibility and accuracy.

Three dimensionally printed nitrocellulose-based microfluidic platform for investigating the effect of oxygen gradient on cells.

In this article, we present a novel nitrocellulose-based microfluidic chip with 3-dimensional (3D) printing technology to study the effect of oxygen gradient on cells. Compared with conventional polydimethylsiloxane (PDMS) chips of oxygen gradient for cell cultures that can only rely on fluorescence microscope analysis, this hybrid nitrocellulose-based microfluidic platform can provide a variety of analysis methods for cells, including flow cytometry, western blot and RT-PCR, because the nitrocellulose-based chips with cells can be taken out from the growth chambers of 3D printed microfluidic chip and then used for cell collection or lysis. These advantages allow researchers to acquire more information and data on the basic biochemical and physiological processes of cell life. The effect of oxygen gradient on the zebrafish cells (ZF4) was used as a model to show the performance and application of our platform. Hypoxia caused the increase of intercellular reactive oxygen species (ROS) and accumulation of hypoxia-inducible factor 1α (HIF-1α). Hypoxia stimulated the transcription of hypoxia-responsive genes vascular endothelial growth factor (VEGF) and induced cell cycle arrest of ZF4 cells. The established platform is able to obtain more information from cells in response to different oxygen concentration, which has potential for analyzing the cells under a variety of pathological conditions.

Near-Infrared Electrochemiluminescence Immunoassay with Biocompatible Au Nanoclusters as Tags.

The design and development of novel electrochemiluminescence (ECL) systems with near-infrared (NIR) emission beyond 800 nm are promising for ECL evolution, especially for improving the throughput of the spectrum-resolved multiplexing ECL assay and biological imaging. Herein a biocompatible and environmentally friendly luminophore, that is, the methionine-stabilized Au nanoclusters (Met-Au NCs), are proposed to achieve efficient aqueous ECL of ∼835 nm with triethanolamine as coreactant. The Met-Au NCs not only demonstrate a 75 times enhanced ECL compared with the traditional Au NCs with bovine serum albumin as a capping agent but also can be employed as ECL tags to label proteins with a methionine linker and enable a highly sensitive NIR ECL bioassay. A sandwich-type NIR ECL immunosensor is constructed with the Met-Au NCs as tags and α-fetoprotein (AFP) as a model analyte and exhibits a wide linearity range from 3 fg·mL-1 to 0.1 ng·mL-1 with a limit of detection of 1 fg mL-1 (S/N = 3) as well as desired selectivity.

A ratiometric electrochemiluminescence method using a single luminophore of porous g-C3N4 for the ultrasensitive determination of alpha fetoprotein.

In this work, we report a simple ratiometric electrochemiluminescence (ECL) method for ultra-sensitive immunoanalysis. A glassy carbon electrode (GCE) was modified by a mixture of porous g-C3N4 nanosheets and carbon nanotubes (CNTs). Secondary antibodies were labeled using CuS nanoparticles as the tags. After immune recognition, CuS nanoparticles in the immunocomplex were dissolved as Cu2+, which can quench the ECL of g-C3N4. The amount of Cu2+ was determined to quantify the concentration of the target antigen. To enhance the sensitivity, Cu2+ ions were firstly enriched and reduced to Cu on the surface of GCE/CNTs-g-C3N4, and the cathodic ECL of g-C3N4 was measured as the reference signal in the ratiometric ECL measurements. After applying a potential of 0.6 V (vs. Ag/AgCl) for 6 s, Cu was dissolved as Cu2+, which can quench the ECL of g-C3N4 with much higher efficiency because the freshly dissolved Cu2+ ions were distributed mainly within the Helmholtz layer of GCE/CNTs-g-C3N4. By using the ECL intensity ratio of GCE/CNTs-g-C3N4 (Cu2+) to GCE/CNTs-g-C3N4 (Cu) measured under the potentiostatic model as the signal indictor, the ratiometric ECL method was used to detect a biomarker of alpha fetoprotein with the limit of detection of 0.1 fg mL-1. It was shown that the influence of the difference in electrode modification and ECL measurement conditions on the determination of Cu2+ is suppressed greatly in the ratiometric ECL method. The combination of ratiometric ECL with electrochemical enrichment and biometallization is a useful strategy to enhance the sensitivity and reproducibility in immunoanalysis.

A differential photoelectrochemical method for glucose determination based on alkali-soaked zeolite imidazole framework-67 as both glucose oxidase and peroxidase mimics.

A differential photoelectrochemical (PEC) method for glucose determination is reported using a nanocomposite with double mimic enzymes of glucose oxidase (GOx) and peroxidase. The nanocomposite was prepared by soaking zeolite imidazole framework-67 (ZIF-67) in 0.1 M NaOH solution at room temperature for 30 min, abbreviated as CoxOyHz@ZIF-67. The Michaelis-Menten constant of CoxOyHz@ZIF-67 to H2O2 and glucose is 121 µM and 3.95 mM, respectively. Using the photoelectrode of CoxOyHz@ZIF-67/TiO2 nanotubes (NTs), glucose was oxidized firstly by dissolved oxygen to generate H2O2 under the catalysis of CoxOyHz film as the mimics of GOx. The product of H2O2 enhanced the photocurrent of TiO2 NTs under the catalysis of ZIF-67 as the mimics of peroxidase. The molecular sieve effect of ZIF-67 frameworks reduces the interferences from molecules with size larger than the apertures in ZIF-67. Under the excitation of a 150 W xenon lamp with full spectrum, the photocurrent was measured in a two-electrode system without external additional potential. By using the photocurrent difference between two photocells, i.e CoxOyHz@ZIF-67/TiO2 NTs and Pt electrode, ZIF-67/TiO2 NTs and Pt electrode, as the signal, the selectivity for glucose determination is improved further. The differential PEC method was applied to the determination of glucose with a linear range 0.1 µM~1 mM and a detection limit of 0.03 µM. Graphical abstract.

Monitoring of reaction kinetics and determination of trace water in hydrophobic organic solvents by a smartphone-based ratiometric fluorescence device.

A smartphone-based ratiometric fluorescence device was designed to monitor the reaction kinetic process under vigorous mixing conditions, demonstrated by the hydrolysis of Cs4PbBr6 nanocrystals (NCs). In the presence of trace water, part of Cs4PbBr6 NCs (non-fluorescent) was converted to CsPbBr3 NCs (strong fluorescent). Using anthracene as the reference fluorophore, the brightness ratio of the green (from CsPbBr3 NCs) to blue (from anthracene) components in the fluorescence image which was recorded in situ by the smartphone camera was measured as the signal for kinetic analysis. It was shown that the water-triggered conversion reaction from Cs4PbBr6 NCs to CsPbBr3 NCs follows the pseudo-second-order kinetic model in the early rapid hydrolysis stage (up to 4 min). With increasing water content, the hydrolysis of Cs4PbBr6 NCs is promoted to yield more CsPbBr3 NCs, which was used to determine trace water in n-hexane, dichloromethane, and toluene with detection limits of 0.031, 0.043, and 0.057 µL mL-1, respectively. The device offers the advantages of portability and low cost for rapid field determination of trace water in hydrophobic organic solvents. Graphical abstract.

Ultrasensitive Electrochemiluminescent Sensor for MicroRNA with Multinary Zn-Ag-In-S/ZnS Nanocrystals as Tags.

For the screening of novel toxic-element-free and biocompatible electrochemiluminophores, electrochemiluminescence (ECL) of multinary nanocrystals (NCs) was investigated for the first time with Zn-Ag-In-S (ZAIS) NCs as model. Aqueous soluble ZAIS NCs could bring out efficient reductive-oxidation ECL with tri- n-propylamine as coreactant, while coating the ZAIS NCs with a ZnS shell could reduce the surface defects of ZAIS NCs, and enable 6.7-fold enhanced ECL of ZAIS/ZnS NCs as compared to ZAIS NCs. ECL of ZAIS/ZnS NCs was about 4.2-fold that of ternary CuInS2/ZnS NCs, spectrally similar to that of Ru(bpy)32+ with maximum emission around 605 nm, and favorable for less electrochemical interference with a lowered triggering potential (∼0.95 V) than that of Ru(bpy)32+. An ultrasensitive ECL microRNA sensor was fabricated with ZAIS/ZnS NCs as tags, which could sensitively and selectively determine microRNA-141 with a wide linearity range from 0.1 fmol/L to 20 pmol/L and a low limit of detection at 50 amol/L ( S/ N = 3). Multinary NCs might provide a promising alternative to the traditional binary NCs for both electrochemiluminophore screening and NC ECL modulating.

Highly luminescent and multi-sensing aggregates co-assembled from Eu-containing polyoxometalate and an enzyme-responsive surfactant in water.

Hybrid co-assembly of polyoxometalates (POMs) with cationic organic matrices offers a preferable way to greatly enhance POM functionality as well as processability. Thus, multi-stimulus responsive supramolecular materials based on lanthanide-containing POMs with improved luminescence may be fabricated from appropriate components through this convenient strategy. Herein, we reported that the co-assembly of Na9(EuW10O36)·32H2O (EuW10) and a commercially available cationic surfactant, myristoylcholine chloride (Myr), in water could produce enhanced red-emitting luminescent aggregates, with their photophysical properties highly dependent on the molar ratio (R) between Myr and EuW10. The R of 36 was finally selected owing to the displayed superior luminescence intensity and good aggregate stability. The Myr/EuW10 hybrids induced by electrostatic and hydrophobic forces presented practically as multilamellar spheres with diameters varying from 80 to 300 nm. Compared to an aqueous solution of EuW10 nanoclusters, a 12-fold increase in absolute luminescence quantum yield (∼23.3%) was observed for the hybrid spheres, which was ascribed to the efficient shielding of water molecules. An unusual aggregation arrangement mechanism and the excellent photophysical properties of these aggregates were thoroughly investigated. Both the enzyme substrate character of Myr and the sensitive coordination structure of EuW10 to the surrounding environment made Myr/EuW10 aggregates exhibit multi-stimulus responsiveness to enzymes, pH, and transition metal ions, thus providing potential applications in fluorescence sensing, targeted-release, and optoelectronics.

A facile synthesis of perforated reduced graphene oxide for high performance electrochemical sensors.

Highly active perforated reduced graphene oxide (P-rGO) was synthesized by a facile methodology based on co-deposition of graphene oxide with sacrificial Prussian blue. Electrode surface properties were characterized by SEM and EDS. The GC/P-rGO electrode exhibited a larger specific surface area than that of GCE. These findings highlighted that the signal was enhanced for both dopamine detection and selenium detection by using P-rGO as a relevant supporting substrate. The result indicated that the large number of perforated structures formed numerous electrically conductive channels in the structure, improving the electrocatalytic properties.

A carbon dot-based fluorescent nanoprobe for the associated detection of iron ions and the determination of the fluctuation of ascorbic acid induced by hypoxia in cells and in vivo.

Maintaining the redox balance of biological systems is a key point to maintain a healthy physiological environment. Excessive iron ions (Fe3+) can cause apoptosis, tissue damage and death. Fortunately, ascorbic acid (AA) as a reducing agent has been evaluated for the reduction of Fe3+. Moreover, AA plays an important role in relieving hypoxia-induced oxidative stress. Therefore, the real-time imaging of the Fe3+ and AA fluctuations is important for understanding their biofunctions in cells and in vivo. In this work, we developed a fluorescent nanoprobe carbon dot-desferrioxamine B (CD-DB) by the conjugate connection of CDs and desferrioxamine B (a complexing agent for Fe3+) for the associated detection of Fe3+ and AA. CD-DB exhibited excellent sensitivity and selectivity for the detection of Fe3+ and AA. The nanoprobe CDs-DB@Fe obtained by the reaction of CD-DB and Fe3+ was suitable for tracing the dynamic changes of AA in cells and in vivo. Therefore, CDs-DB@Fe was used for monitoring the fluctuation of AA in hypoxic cell models, hypoxic zebrafish models and liver ischemia mice models. These results exhibited the decrease in AA under hypoxic conditions because AA was consumed to neutralize free radicals and relieve hypoxia-induced oxidative stress damage. The ideal biocompatibility and low toxicity make our nanoprobe a potential candidate for the research of the physiological effects of AA in vivo.

A ratiometric electrochemical sensor for multiplex detection of cancer biomarkers using bismuth as an internal reference and metal sulfide nanoparticles as signal tags.

Ratiometric electrochemical sensors can provide a relatively accurate analysis of target analytes due to their self-calibration function. Herein, we report a simple ratiometric strategy for achieving the electrochemical detection of Cd(ii), Hg(ii), Pb(ii) and Zn(ii), as well as multiple cancer biomarkers by using metal sulfide nanoparticles as signal tags. A conductive polymer film of poly(2-amino terephthalic acid) (ATA) was electrochemically produced on a glassy carbon electrode (GCE) and doped with carbon nanotubes (CNTs) and mercaptosuccinic acid (MSA). Using Bi(iii) as an enhancer and internal reference in anodic stripping voltammetry, the MSA-CNT-ATA/GCE exhibited sensitive and distinguishable voltammetric responses to Cd(ii), Hg(ii), Pb(ii) and Zn(ii), with detection limits of 0.13, 0.49, 0.16 and 0.089 µg L-1, respectively. By using CdS, HgS, PbS and ZnS labeled secondary antibodies as the signal tags, alpha-fetoprotein, carbohydrate antigen 19-9, carbohydrate antigen 125, and carcinoembryonic antigen were determined simultaneously according to the amounts of metal sulfide in the sandwich-type complexes, with detection limits of 0.11 pg mL-1, 0.68 mU mL-1, 1.4 mU mL-1 and 0.23 pg mL-1, respectively. This ratiometric approach has a wide scope in the electrochemical detection of heavy metal ions as well as immunoassays with metal ions serving as signal tags.

Electrochemical-Signal-Amplification Strategy for an Electrochemiluminescence Immunoassay with g-C3N4 as Tags.

Signal amplification for electrochemiluminescence (ECL) has conventionally been achieved by employing effective matrixes that can accelerate the electrochemical redox processes or carry more electrochemiluminophores. Herein, a convenient signal-amplification strategy was proposed for an ECL immunoassay with carboxylated g-C3N4 nanosheets (NSs) as tags and carcinoembryonic antigen (CEA) as the model target via electrochemically pretreating the substrate: a glassy-carbon electrode (GCE) modified with a polymerized 2-aminoterephthalic acid (ATA) film (GCE/ATA). Bioconjugates of g-C3N4 NSs and the signal CEA antibody (Ab2) (i.e., g-C3N4 NS-Ab2) were immobilized on GCE/ATA via a sandwich immunoreaction to form GCE/ATA-Ab1-Ag-Ab2-NSs. Electrochemical-impedance spectroscopy and potential-resolved ECL characterization proved that GCE/ATA plays an important role in the electron-transfer resistance ( Ret) of the GCE/ATA-Ab1-Ag-Ab2-NSs for ECL and that successively scanning GCE/ATA-Ab1-Ag-Ab2-NSs from 0 to -1.6 V in K2S2O8- and H2O2-containing medium could reduce the Ret and bring out 3.3-times-enhanced ECL at the 10th scan cycle compared with that of the 1st scan cycle, which was about 10.2 times the ECL of the GCE/ATA-Ab1-Ag-Ab2-NSs in medium containing merely K2S2O8. Inspired by this, direct and successive scanning of GCE/ATA in K2S2O8- and H2O2-containing medium was employed during fabrication, which dramatically reduced the Ret of GCE/ATA-Ab1-Ag-Ab2-NSs and brought out obviously enhanced ECL responses for selectively determining CEA from 0.1 pg/mL to 1 ng/mL, with a detection limit of 3 fg/mL.

Unfound Associated Resonant Model and Its Impact on Response of a Quartz Crystal Microbalance in the Liquid Phase.

Quartz crystal microbalance (QCM) is an important tool to detect in real time the mass change at the nanogram level. However, for a QCM operated in the liquid phase, the Sauerbrey equation is usually disturbed by the changes in liquid properties and the longitudinal wave effect. Herein, we report another unfound associated high-frequency resonance (HFR) model for the QCM, with the intensity 2 orders of magnitude higher than that of the fundamental peak in the liquid phase. The HFR model exhibits obvious impact on the response of QCM in the thickness-shear model (TSM), especially for overtones. The frequency of HFR peak is decreased dramatically with increasing conductivity or permittivity of the liquid phase, resulting in considerable additional frequency shifts in the TSM as baseline drift. Compared to that with a faraway HFR peak, the overlapping of HFR peak to a TSM overtone results in the frequency shifts of ±50-70 kHz with its intensity enhancement by 3 orders of magnitude in the later. The HFR behavior is explained by an equivalent circuit model including leading wire inductance, liquid inductance, and static capacitance of QCM. Taking into account the HFR model, the positive frequency shifts of the QCM at high overtones during the cell adhesion process is understandable. Combining the TSM and HFR is an effective way to improve the stability of QCM and provides more reliable information from the responses of QCM. The HFR may have potential application in chemical and biological sensors.

Flexible and enhanced multicolor-emitting films co-assembled by lanthanide complexes and a polymerizable surfactant in aqueous solution.

Lanthanide complex doped lyotropic liquid crystals (LLCs) are soft materials which are impressive due to their excellent luminescence efficiencies and stabilities. The introduction of lanthanide complexes into polymerizable LLCs, however, may produce organized films with better optical and mechanical properties through in situ photopolymerization. An environmentally friendly strategy to fabricate flexible multicolor-emitting films has been developed through co-assembling red-/green-emitting trisdipicolinate lanthanide complexes [choline]3[Ln(DPA)3] (Ln-DPA, Ln = Eu, Tb) into LLC matrices mainly via electrostatic interaction and further photopolymerization. The LLCs were constructed from a polymerizable surfactant, 3-dodecyl-1-vinylimidazolium bromide (C12VIMBr), in aqueous solution. The maintenance of the well-defined LLC nanostructures in the luminescent films was validated by small-angle X-ray scattering (SAXS) as well as scanning electron microscopy (SEM) measurements. Remarkably, the lifetime and absolute luminescence quantum efficiency of such films have been improved significantly compared with those of the corresponding solid Eu-DPA complex or in aqueous solution and LLC matrices. Through tuning the molar ratio of Eu-DPA to Tb-DPA complexes, the emission color of the films could be finely-tailored between red and green in the CIE chromaticity diagram. Furthermore, the films also possessed certain mechanical strength and stability against pH, metal ions, and temperature, indicating their potential application as robust luminescent materials.

A ratiometric photoelectrochemical immunosensor based on g-C3N4@TiO2 NTs amplified by signal antibodies-Co3O4 nanoparticle conjugates.

Herein, we report a ratiometric photoelectrochemical (PEC) immunosensor coupled with secondary antibodies-Co3O4 nanoparticle conjugates (Ab2-Co3O4 NPs) for signal amplification. The Ab1-g-C3N4@TiO2 NTs and BSA-g-C3N4@TiO2 NTs act as the sensing and reference photoelectrodes, where Ab1, BSA and TiO2 NTs are the capture antibodies, bovine serum albumin and TiO2 nanotube arrays, respectively. In the presence of target Ag, the sensing PEC photocurrent decreases due to the steric hindrance of Ab1 molecules, which increases the inner resistance of the photoelectrode. The signal-off response is enhanced further using Ab2-Co3O4 NP conjugates due to their steric hindrance effect and the consumption of electron donors by the Co3O4 NPs. Furthermore, the performance of the ratiometric PEC platform is tested using alpha-fetoprotein (AFP) as a model antigen. Under the optimal conditions, the concentration of AFP is detected in the range of 0.4 pg mL-1 to 40 ng mL-1 with a detection limit of 0.2 pg mL-1. This ratiometric strategy is beneficial to improve the reliability and anti-interference ability of PEC immunosensors.

A smartphone-based double-channel fluorescence setup for immunoassay of a carcinoembryonic antigen using CuS nanoparticles for signal amplification.

Sensitive detection of cancer biomarkers is valuable for clinical diagnosis and treatment assessment of cancers. Herein, we report a simple smartphone-based double-channel fluorescence setup for immunoassay. Not including the smartphone, the total cost of the detection device itself is about 80 $, including a laser pointer, a twinning measurement cell, a collective lens, and an outside box. The fluorescence images of the sample and reference areas were captured by the camera in the smartphone and the brightness ratio was calculated using a user-edited smartphone app. By using 2,3-diaminophenazine (DAP) as the model luminophore, the influence of exposure time and photosensitivity on the sensitivity was tested. The brightness ratio offers high stability of the fluorescence signal, which is helpful to improve the sensitivity. The applicability of this device was demonstrated by a catalytic fluorimetric method for Cu2+ determination, which is based on the oxidation of o-phenylenediamine (non-fluorescent) to DAP (strong fluorescent) by dissolved oxygen using Cu2+ as the catalyst. Accordingly, by using a CuS nanoparticle-conjugated second antibody as the signal tag, the immunoassay for a carcinoembryonic antigen was performed with the detection limit of 0.05 pg mL-1. This smartphone-based double-channel fluorescence device offers the advantages of high sensitivity, inexpensive and miniaturization.

Voltammetric determination of copper in seawater at a glassy carbon disk electrode modified with Au@MnO2 core-shell microspheres.

Anodic stripping voltammetric determination of copper ions was accomplished at a glassy carbon disk electrode modified with core-shell microspheres of the gold@manganese dioxide (Au@MnO2) type. These were synthesized via electrochemical deposition. The gold nanoparticles (AuNPs) were electrochemically deposited and employed as an active support material for the growth of MnO2 to yield Au@MnO2 core-shell particles with unique and regular spherical morphology. The microspheres have a diameter of 200-250 nm and scrolled edges like a cactus. Due to the absorption capacity of MnO2 and the electrocatalytic ability of the AuNPs, an excellent anodic signal is obtained for copper ions. Response is linear in the 20 nM to 1 µM copper ion concentration range, with a 4.9 ± 0.2 nM (n = 3) detection limit under optimized conditions. The electrode is stable and excellently reproducible. It was successfully applied to the analysis of copper ions in spiked seawater samples. Graphical abstract Gold nanoparticles were employed as a coupling medium for the bridging of MnO2 on a glassy carbon disk electrode to transfer electrons that enhanced electrochemical detection of copper ions.