Ultrasensitive Detection of SARS-CoV-2 Nucleocapsid Protein Based on Porphyrin-Based Metal-Organic Gels with Highly Efficient Electrochemiluminescence at Low Potential.

Metal-organic gels (MOGs) are a new type of intelligent soft material, which are bridged by metal ions and organic ligands through noncovalent interactions. In this paper, we prepared highly stable P-MOGs, using the classical organic electrochemiluminescence (ECL) luminescence meso-tetra(4-carboxyphenyl)porphine as the organic ligand and Fe3+ as the metal ion. Surprisingly, P-MOGs can stably output ECL signals at a low potential. We introduced P-MOGs into the ECL resonance energy transfer strategy (ECL-RET) and constructed a quenched ECL immunosensor for the detection of the SARS-CoV-2 nucleocapsid protein (SARS-CoV-2-N). In the ECL-RET system, P-MOGs were used as energy donors, and Au@Cu2O@Fe3O4 were selected as energy acceptors. The ultraviolet-visible spectrum of Au@Cu2O@Fe3O4 partially overlaps with the ECL spectrum of P-MOGs, which can effectively touch off the ECL-RET behavior between the donors and receptors. Under the ideal experimental situation, the linear detection range of the SARS-CoV-2-N concentration was 10 fg/mL to 100 ng/mL, and the limit of detection was 1.5 fg/mL. This work has broad application prospects for porphyrin-MOGs in ECL sensing.

Controlled-Release Electrochemiluminescence Biosensor with Strong Self-On Effect by a Multiple Signal Amplification Strategy for Trace Detection of Prostate-Specific Antigen.

The enhancement of sensitivity in biological analysis detection can reduce the probability of false positives of the biosensor. In this work, a novel self-on controlled-release electrochemiluminescence (CRE) biosensor was designed by multiple signal amplification and framework-enhanced stability strategies. As a result, the changes of the ECL signal were enhanced before and after the controlled-release process, achieving sensitive detection of prostate-specific antigen (PSA). Specifically, for one thing, Fe3O4@CeO2-NH2 with two paths for enhancing the generation of coreactant radicals was used as the coreaction accelerator to boost ECL performance. For another, due to the framework stability, zeolitic imidazolate framework-8-NH2 (ZIF-8-NH2) was combined with luminol to make the ECL signal more stable. Based on these strategies, the constructed CRE biosensor showed a strong self-on effect in the presence of PSA and high sensitivity in a series of tests. The detection range and limit of detection (LOD) were 5 fg/mL to 10 ng/mL and 2.8 fg/mL (S/N = 3), respectively, providing a feasible approach for clinical detection of PSA.

Double-Amplified Electrochemiluminescence Immunoassay Sensor for Highly Sensitive Detection of CA19-9 Using a Ternary Semiconductor CdSSe.

In this paper, an electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of CA19-9 was constructed using ternary compound CdSSe nanoparticles as ECL emitter. The immunosensor employs Cu2S and gold-doped diindium trioxide (Au-In2O3) nanocubes as coreaction accelerators to achieve a double-amplification strategy. In general, a hexagonal maple leaf-shaped Cu2S with a large surface area was selected as the template, and the in situ growth of CdSSe on its surface was achieved using a hydrothermal method. The presence of Cu2S not only inhibited the aggregation of CdSSe nanoparticles to reduce their surface energy but also acted as an ECL cathode coreaction promoter, facilitating the generation of SO4•-. Consequently, the ECL intensity of CdSSe was significantly enhanced, and the reduction potential was significantly lower. In addition, the template method was employed to synthesize Au-In2O3 nanocubes, which offers the advantage of directly connecting materials with antibodies, resulting in a more stable construction of the immunosensor. Furthermore, In2O3 serves as a coreaction promoter, enabling the amplification strategy for ECL intensity of CdSSe, thus contributing to the enhanced sensitivity and performance of the immunosensor. The constructed immunosensor exhibited a wide linear range (100 µU mL-1 to 100 U mL-1) and a low detection limit of 80 µU mL-1, demonstrating its high potential and practical value for sensitive detection of CA19-9.

Negative Linear Compressibility and Interlayer Gap Closure in Layered Rare-Earth Hydroxyhalide (YCl(OH)2) under High Pressure.

Layered materials have attracted extensive attention due to their exceptional physical and chemical properties. Understanding the structural evolution of such materials under high pressure is crucial for the development of new functional materials. In this study, the structure evolution of the synthesized layered rare-earth hydroxyhalide YCl(OH)2 under high pressures up to approximately 9.4 GPa was explored by using a diamond anvil cell combined with synchrotron single-crystal X-ray diffraction. Simultaneously, high-pressure Raman spectroscopy experiment was conducted to 10.3 GPa. Our findings indicate that YCl(OH)2 maintains its symmetry within the experimental pressure range. The pressure-volume data of YCl(OH)2 were fitted to the third-order Birch-Murnaghan equation of state (EoS) to derive its EoS parameters including zero-pressure unit-cell volume (VT0), isothermal bulk modulus (KT0), and its pressure derivative (K'T0): VT0 = 142.47 (1) Å3, KT0 = 38.2 (18) GPa, and K'T0 = 9.8 (1). However, the unit-cell parameters a, b, and c exhibit a distinct compressional behavior, with the a-axis being the most compressible and the b-axis being the least. Particularly noteworthy is the observation that YCl(OH)2 displays a negative linear compressibility along the b-axis within the pressure range of 0.4-5.3 GPa. Further detailed structure refinement and Raman spectroscopy analyses indicate that the anomalous behavior of the b-axis could be attributed to the formation of the O-H···O hydrogen bonding chains along the b direction. Moreover, the coordination number of Y3+ increased from 8 to 9 as the pressure reached 5.3 GPa due to the reduction of the interlayer spacing upon compression, ultimately leading to the closure of the interlayer gap.

Self-powered photochemical cathode aptamer sensor based on ZnIn2S4 photoanode and Cu2O@Ag@Ag3PO4 photocathode for the sensitive detection of Hg2.

A self-powered photoelectrochemical (PEC) aptamer sensor based on ZnIn2S4 as the photoanode and Cu2O@Ag@Ag3PO4 as the sensing cathode is designed for the detection of Hg2+. An indium tin oxide (ITO) electrode modified with ZnIn2S4 was used instead of a platinum (Pt) counter electrode to provide an obviously stable photocurrent signal. The suitable band gap width of ZnIn2S4 can generate photogenerated electrons well. The unique hydrangea structure of ZnIn2S4 can enhance light absorption and accelerate the separation and transfer of photocarriers. At the same time, Cu2O@Ag@Ag3PO4 with excellent electrical conductivity further enhances the photocurrent provided by the ZnIn2S4 photoanode. Because the reducing substances in the biological medium can change the photoanode characteristics of the photoanode interface, the separation of the photoanode and the sensing bicathode is beneficial to improve the anti-interference ability of the sensor. Under optimized conditions, the PEC aptamer sensor realizes the detection of Hg2+ (1 mM-1 fM), and the detection limit is 0.4 fM. In addition, the constructed self-powered PEC sensor has good selectivity, repeatability, and stability, which provides a new idea for the design of the PEC aptamer sensor platform.

Aggregation-Induced Electrochemiluminescence Frame of Silica-Confined Tetraphenylethylene Derivative Matrixes for CD44 Detection via Peptide Recognition.

The theory of aggregation-induced electrochemiluminescence (AIECL) has introduced new vitality into preparing new electrochemiluminescence (ECL) emitters. However, the progress in the application of biosensing analysis has been slow owing to the lack of AIECL-based functional nanomaterials. Herein, a biosensor was fabricated using mesoporous silica nanosphere (MSN) matrix-confined 1,1,2,2-tetra(4-carboxylphenyl)ethylene (TPE) as a well-ordered ECL emitter and self-designed WHPWSYC (WC-7) heptapeptide as the target capturer for CD44 detection. TPE and its co-reactant, triethylamine (TEA), were encapsulated in the MSN nanomatrix to enhance the radiation transition by limiting the intramolecular rotation of TPE molecule benefit from the spatial confinement effect, and the ECL intensity is self-enhanced by replacing electron free diffusion in the conventional ECL system. MSN-TPE-TEA can act as satisfactory sensing substrates that improve the reproducibility and batch-to-batch consistency of biosensors and functions as a stable signal label for trace analysis of biomarkers. As a substitute for antibody and hyaluronic acid, the WC-7 heptapeptide significantly reduced the steric hindrance of the sensing interface in CD44 affinity tests. Combined with the DNA strand displacement reaction, this strategy shows a good ECL response to standard CD44 antigen and MCF-7 cells with different concentrations, which is another feasible method for detecting CD44 in body fluids or living cells.

Highly Efficient Signal On/Off Electrochemiluminescence Gel Aptasensor Based on a Controlled Release Strategy for the Sensitive Detection of Prostate Specific Antigen.

The controlled release strategy can make the constructed sensor have the function of self-on/off, which has an obvious effect on improving the sensitivity in immunoassays. Metal organic gels (MOGs) are the most noteworthy. They are materials with ultrahigh surface area, highly dispersed atomical metal sites, and well-defined porosity and can be used as an efficient luminophore to cause the developed sensor to have good hydrophilicity and adjustability, thus further improving the detection sensitivity. In this work, a novel on/off electrochemiluminescence (ECL) gel aptasensor was constructed using the Cys-[Ru(dcbpy)3]2+ gel as a luminophore, ZnS quantum dots (QDs) as quenchers, and aminated mesoporous silica nanocontainers (SiO2-NH2) as carriers of controlled release for prostate specific antigen (PSA) detection. Specifically, the ssDNA and PSA aptamer made up clamp-like molecules to block holes of the SiO2-NH2 after encapsulating the quencher ZnS QDs. Because of the specific binding between the PSA antigen and aptamer, the clamp-like molecules of ssDNA and the PSA aptamer were disassembled. Finally, the release of ZnS QDs was triggered, thereby realizing a self-off mode of the ECL signals under a co-reactant-free environment by ECL resonance energy transfer (ECL-RET) between the Cys-[Ru(dcbpy)3]2+ and ZnS QDs. In addition, the quenching mechanism was confirmed by molecular orbitals from the theoretical calculation level. The detection limit of the gel aptasensor for PSA was as low as 1.01 fg/mL, showing excellent sensitivity and accuracy. These strategies provided a feasible idea for PSA and even other tumor marker immunoassays.

Magnetically Controlled and Addressable Photoelectrochemical Sensor Array with Self-Calibration for the Label-Free Detection of Amyloid ß-Proteins.

A label-free addressable photoelectric immunosensor array was designed for the detection of amyloid ß-proteins based on magnetic separation and self-calibration strategies. In this paper, Na2Ti6O13 with a flower-like morphology was prepared by the hydrothermal method; after continuously combining Fe3O4 and CdS, it was endowed with magnetism and better photoelectric activity. Subsequently, a series of reactions occurred in the solution, and the magnetic separation method was used to enrich the target. On the other hand, the ITO glass was separated into eight sites (2 × 4) using magnets, and a light shield was utilized to prevent light exposure, resulting in addressable and continuous detection. After the uniform preparation of magnetic photoelectric materials and precise control of testing conditions, the relative errors among different sites have been effectively reduced. Moreover, incorporating a self-calibration strategy has allowed the sensor array to achieve greater accuracy. The proposed photoelectrochemical biosensor exhibits a good relationship with amyloid ß-protein ranging from 0.01 to 100 ng mL-1 with a limit of detection of 1.1 pg mL-1 and exhibits excellent specificity, reproducibility, and stability.

Controlled Growth of MoS2 on Dendritic Ferric Oxide to Enhance Electrochemiluminescence of Nitrogen-Doped Carbon Quantum Dots for Sensitive Immunoassay.

The essential expansion of electrochemiluminescence (ECL) technology into clinical detection relies on sensitive and stable signal and maintenance of the activity of the immune molecules during the analysis. This poses a critical challenge for an ECL biosensor as a luminophore in general requires high potential excitation resulting in a strong ECL signal; nevertheless, it has an irreversible effect on the activity of the antigen or antibody. Herein, a novel electrochemiluminescence (ECL) biosensor utilizing nitrogen-doped carbon quantum dots (N-CQDs) as emitters and molybdenum sulfide/ferric oxide (MoS2@Fe2O3) nanocomposites as a coreaction accelerator was developed for detection of neuron-specific enolase (NSE), a biomarker of small cell lung cancer. The doping of nitrogen allows the CQDs to exhibit ECL signals with low excitation potential, with a more viable activity possible for immune molecules. MoS2@Fe2O3 nanocomposites exhibit superior coreaction acceleration characteristics in hydrogen peroxide than any single component of them, and the highly branched dendrite microstructure provides a large number of binding sites for immune molecular, which is an inevitable factor for trace detection. In addition, ion beam sputtering gold particle technology is introduced into the sensor fabrication via an Au-N bond, which will provide sufficient density orientation for capturing the antibody load via the Au-N bonds. With excellent repeatability, stability, and specificity, the as-purposed sensing platform showed differentiated ECL responses of NSE range from 10.00 fg/mL to 500 ng/mL, and the limit of detection (LOD) was calculated of 6.30 fg/mL (S/N = 3). The proposed biosensor is prospective to provide a new avenue for the analysis of NSE or other biomarkers.

A photoelectrochemical sensor for Hg2+ detection with enhanced cathodic photocurrent via BiOI/Bi2S3 photoanode of self-sacrifice.

Due to the inherent merits of the anodic photoelectrochemical (PEC) sensor, it was widely utilized in the field of analytical chemistry. However, it must be noted that the anodic PEC sensor was susceptible to interference in practical applications. The situation with the cathodic PEC sensor was exactly the opposite. Therefore, this work fabricated a PEC sensor combining photoanode and photocathode that solved the defects of conventional PEC sensors in detecting Hg2+. Specifically, Na2S solution was carefully dropped on the BiOI-modified indium-tin oxide (ITO) to obtain ITO/BiOI/Bi2S3 directly by self-sacrifice method and the resulting electrode was used as photoanode. In addition, a sequential modification process was employed to decorate the ITO substrate with Au nanoparticles (Au NPs), Cu2O, and L-cysteine (L-cys), thereby realizing the fabrication of the photocathode. Moreover, the presence of Au NPs further amplified the photocurrent of the PEC platform. During the detection process, when Hg2+ is present it will bind to the L-cys, resulting in an increase in current, thus enabling sensitive detection of Hg2+. The proposed PEC platform exhibited good stability and reproducibility, providing a new idea for the detection of other heavy metal ions.

Cu2O@PdAg-quenched CdS@CeO2 heterostructure electrochemiluminescence immunosensor for determination of prostate-specific antigen.

Based on the resonance energy transfer between CdS@CeO2 and Cu2O@PdAg, a quenching immunosensor for sensitive detection of prostate specific antigen (PSA) was constructed. The CdS@CeO2 heterostructure was obtained by in situ growth of CeO2 particles on the surface of CdS nanorods, and stable cathodic ECL emission was achieved using K2S2O8 as coreactant. Cu2O@PdAg was composed of Cu2O with tetradecahedral structure and bimetallic PdAg nanospheres and has a UV-V is absorption range between 600 and 800 nm. It overlaps with the ECL emission spectrum of CdS@CeO2, realizing the effective quenching of the ECL signal, which provides feasibility for subsequent practical application. The immunosensor exhibited good linearity in the concentration range 10 fg·mL-1 ~ 100 ng·mL-1, with a detection limit of 5.6 fg·mL-1. In sample analysis, the recoveries were 99.8-101%, and the relative standard deviation (RSD) was 0.85-1.6% showing great potential and development value for the sensitive detection of prostate cancer.

Hollow Double-Shell CuCo2O4@Cu2O Heterostructures as a Highly Efficient Coreaction Accelerator for Amplifying NIR Electrochemiluminescence of Gold Nanoclusters in Immunoassay.

The evolution of electrochemiluminescence (ECL) emission amplified by coreaction accelerator in near-infrared (NIR) area has been overwhelmingly anticipated for ultrasensitive detection of disease biomarkers. Herein, the hollow double-shell CuCo2O4@Cu2O (HDS-CuCo2O4@Cu2O) heterostructures were conveniently prepared and utilized as an attractive coreaction accelerator to improve the NIR ECL performance of gold nanoclusters (AuNCs) for the first time. Benefiting from perfect-matched lattice spacing, unique Cu2O nanoparticles (NPs) were formed in situ on the layered-hollow CuCo2O4 nanospheres (NSs) to obtain HDS-CuCo2O4@Cu2O heterostructures. The formed heterojunctions supplied shorter charge transfer distance and better interfacial charge transfer efficiency as well as more effective separation performance. Consequently, HDS-CuCo2O4@Cu2O heterostructures as an admirable electroactive substrate could significantly promote the formation of sufficient coreactant intermediate radicals to react with AuNCs cationic radicals, realizing about 3-folds stronger NIR ECL response than that of individual AuNCs. In addition, the AuNCs templated by l-methionine (l-Met) exhibited NIR ECL emission around 830 nm, which could decrease the photochemical damage to even realize a nondestructive detection with improved susceptibility and circumambient adaptability. Subsequently, a well site-oriented fixation strategy utilizing HWRGWVC heptapeptide as the specific antibody immobilizer was introduced to further preserve the bioactivity of antibody on the HDS-CuCo2O4@Cu2O and AuNCs surface along with enhancing the incubation performance markedly. In view of the progressive sensing mechanism, a NIR immunosensor was obtained for the ultrasensitive analysis of CYFRA21-1, which achieved a broad linear ranging from 2 fg/mL to 50 ng/mL and a low limit of detection (LOD) of 0.67 fg/mL (S/N = 3).

Addressable Label-Free Photoelectric Sensor Array with Self-Calibration for Detection of Neuron Specific Enolase.

An addressable label-free photoelectric immunosensor array was designed for detection of neuron specific enolase (NSE) based on TiO2/CdS as substrate materials. In this work, the hydrothermal synthesized TiO2 nanorod film is evenly grown on the surface of the fluorine-doped tin oxide (FTO), and then CdS with a narrow band gap is added for sensitization through successive ionic layer adsorption reactions. The obtained TiO2/CdS composite materials with matched energy band structures promote the rapid electron transfer and effectively reduce the recombination of electron hole pairs, which greatly enhance the visible light absorption and increased photocurrent intensity. In order to construct a suitable sensor array, the sensitized FTO electrode is divided into multiple regions of equal size by insulating stickers, and then the addressable and continuous detection of multiple samples can be achieved. Because multiple detection regions are prepared and tested under the same conditions, the difference effectively reduces, and the sensor can realize self-calibration and obtain more accurate results. Under optimal conditions, this sensor array can detect NSE in the linear range of 0.01-100 ng mL-1 with a detection limit of 2.49 pg mL-1 (S/N = 3). The sensor array has good selectivity, stability, and reproducibility, making it a viable approach for real sample detection.

Novel Photoelectrochemical Biosensing Platform Based on a Double Type II CdLa2S4/SnIn4S8/Sb2S3 Ternary Heterojunction as Photoactive Materials and NiCo2O4 Nanospheres as a Photoquencher for CA19-9 Detection.

A novel signal-off biosensing platform based on the CdLa2S4/SnIn4S8/Sb2S3 heterojunction as photoactive materials and NiCo2O4 nanospheres as a photoquencher was developed to achieve the sensitive detection of CA19-9. First, the narrow band gap hydrangea-like CdLa2S4/SnIn4S8/Sb2S3 not only provided excellent photocurrent response but also supplied a mass of active sites that facilitated the loading of capture antibody (Ab1). Second, a double type II CdLa2S4/SnIn4S8/Sb2S3 heterojunction promoted the fast separation and migration of photogenerated e-/h+ and overcame the problem of short carrier lifetime caused by the recombination of photogenerated carriers. In addition, to improve the sensitivity of the constructed sensor to detect CA19-9, signal tags (p-type NiCo2O4) with large steric hindrance were introduced to accomplish signal amplification by the effect of double signal quenching. On one hand, NiCo2O4, which was strongly responsive to visible light, utilized its own advantages to compete for AA with CdLa2S4/SnIn4S8/Sb2S3, resulting in a decrease in the hole scavenging rate of the substrate. On the other hand, the photoquencher NiCo2O4 also prevented AA from contacting the matrix and further aggravated the photoelectrochemical (PEC) signal-damping effect. The PEC immunosensor was prepared with brilliant selectivity and splendid stability to detect CA19-9 (0.001-50 U/mL), and the detection limit was 0.0004 U/mL (S/N = 3).

Rare Self-Luminous Mixed-Valence Eu-MOF with a Self-Enhanced Characteristic as a Near-Infrared Fluorescent ECL Probe for Nondestructive Immunodetection.

Steady and efficient sensitized emission of Eu2+ to Eu3+ can be achieved through a rare mixed-valence Eu-MOF (L4EuIII2EuII). Compared with the sensitization of other substances, the similar ion radius and configuration of the extranuclear electron between Eu2+ and Eu3+ make sensitization easier and more efficient. The sensitization of Eu2+ to Eu3+ is of great assistance for the self-enhanced luminescence of L4EuIII2EuII, the longer luminous time, and the more stable electrochemiluminescence (ECL) signal. Simultaneously, L4EuIII2EuII possesses near-infrared (NIR) fluorescence of around 900 nm and a mighty self-luminous characteristic, which render it useful as a NIR fluorescent probe and as a luminophore to establish a NIR ECL biosensor. This NIR biosensor can greatly reduce the damage to the detected samples and even achieve a nondestructive test and improve the detection sensitivity by virtue of strong susceptibility and environmental suitability of NIR. In addition, the CeO2@Co3O4 triple-shelled microspheres further enhanced the ECL intensity due to two redox pairs of Ce3+/Ce4+ and Co2+/Co3+. The NIR ECL biosensor based on these strategies owns an ultrasensitive detection ability of CYFRA 21-1 with a low limit of detection of 1.70 fg/mL and also provides a novel idea for the construction of a highly effective nondestructive immunodetection biosensor.

Facile Encapsulation of Iridium(III) Complexes in Apoferritin Nanocages as Promising Electrochemiluminescence Nanodots for Immunoassays.

A class of water-soluble electrochemiluminescence (ECL) nanodots were prepared by encapsulating ECL-active iridium complexes into biocompatible horse spleen apoferritin (apoHSF) nanocages for immunoassays. The preparation feasibility was achieved based on the pH-induced disassembly/reassembly nature originated from apoHSF. Two iridium nanodots (1 and 2) with high ECL efficiency were separately prepared by directing the self-assembly of two water-insoluble luminescent complexes, Ir(ppy)3 (ppy = 2-phenylpyridine) and Ir(ppy)2(acac) (ppy = 2-phenylpyridine and acac = acetylacetonate), in the apoHSF cavity. Using tri-n-propylamine (TPrA) as a coreactant, the electrochemistry and "oxidative-reductive" ECL mechanisms for nanodots 1 and 2 were investigated, respectively. After demonstrating the spectroscopic property and relative ECL efficiency, the ECL emission of nanodots 1 and 2 quenched by TPrA• radicals at high potential was further studied and circumvented by optimizing the potential range and TPrA concentration for generating strong and stable ECL emission in aqueous media. The well-inherited biological functions of apoHSF in nanodots allow the convenient external modification of an antibody to act as a signal probe, thus a versatile ECL immunoassay paradigm was established. Acceptable results from this assay enabled the rapid and accurate detection of biomarkers in real samples. The unprecedented use of apoHSF is feasible and applicable for water-insoluble iridium complexes to fabricate a wide variety of biocompatible ECL nanodots for potential bioanalysis.

Self-Powered Cathodic Photoelectrochemical Aptasensor Comprising a Photocathode and a Photoanode in Microfluidic Analysis Systems.

An intriguing self-powered cathodic photoelectrochemical (PEC) microfluidic aptasensor with enhanced cathodic photocurrent response is proposed for sensitive detection of prostate-specific antigen (PSA). The self-powered system is constructed by a cadmium sulfide-sensitized zinc oxide nanorod array (CdS/ZnO NA) as a photoanode with an iodide-doped bismuth oxychloride flower-array (I0.2:BiOCI0.8) as a photocathode, which can generate the electrical output under visible light irradiation with no external power supply. In addition, the p-type semiconductor I0.2:BiOCI0.8 with a special internal electric field between the iodide ion layer and the [Bi2O2]2+ layer could increase the cathodic photocurrent response by facilitating the separation of electron/hole pairs under visible light excitation. It is worth noting that dissolved oxygen as an electron acceptor can be reduced by the photogenerated electron to form a superoxide radical (•O2-) in the self-powered cathodic PEC system. The further enhanced cathodic photocurrent response can be achieved by eliminating •O2- that reacts with the luminol anion radical (L•-) to produce chemiluminescence emission, which serves as an inner excitation light source. What is more exciting is that the integration of the photoanode and the photocathode into a microfluidic chip could realize automatic sample injection and detection. On this basis, the proposed aptasensor presents excellent reproducibility and high sensitivity for detecting PSA and exhibits a good linearity range (50 fg·mL-1 to 50 ng·mL-1) with a low detection limit (25.8 fg·mL-1), which opens up a new horizon of potential for sensitively detecting other kinds of disease markers.

A dual signal-amplified electrochemiluminescence immunosensor based on core-shell CeO2-Au@Pt nanosphere for procalcitonin detection.

A dual signal-amplified sandwich electrochemiluminescence (ECL) immunosensor was fabricated for trace detection of procalcitonin (PCT). CeO2-Au@Pt composed of sea urchin-like Au@Pt nanoparticles coated on CeO2 hollow nanospheres was immobilized on electrode surface to electrochemically catalyze H2O2 to produce a large number of superoxide anion (O2•-). The immunosensor was prepared by linking the capture antibody on immobilized CeO2-Au@Pt with heptapeptide (HWRGWVC), which could maintain the activity of the antibody. The prepared Au star@BSA was used to bind abundant luminol for labeling the secondary antibody (Ab2). Upon the sandwich-typed immunoreactions, the O2•- could react with the introduced luminol on the immunosensor surface to produce strong ECL intensity. With an outstanding linear detection range and a low detection limit of 17 fg/mL, the ECL immunosensor permitted ultrasensitive detection of PCT at a low H2O2 concentration and demonstrated its high application potential in the clinical assay.

Liposome encapsulated electron donor strategy for signal-on CYFRA 21-1 photoelectrochemical analysis.

A novel electron donor controlled-release system is proposed based on liposome encapsulated L-cysteine for the sensitive determination of cytokeratin 19 fragment 21-1 (CYFRA 21-1). On the one hand, a defective TiO2 modified with methylene blue was employed as a photoactive platform which exhibited a high photoelectrochemical (PEC) response owing to the introduction of oxygen vacancies and the high  photosensitivity of the dye. On the other hand, L-cysteine as the sacrificial electron donor was encapsulated in the vesicles of liposomes, and this composite was used as the signal amplification factor, which is labeled on the secondary antibody of CYFRA 21-1 to further improve the photocurrent sensitivity. The excellent electron transfer path in photoactive materials coupled with the skilful electron donor controlled-release system, contributed to the sensitive  PEC analysis of CYFRA 21-1 underoptimum conditions. The PEC immunoassay showed a linear current response in the range 0.0001-100 ng/mL with a detection limitof 37 fg/mL. Enhanced stability and satisfactory reproducibility were also achieved. The proposed concept  provides a novel signal-on strategy for the sensitive detection of other cancer markers in the electrochemical sensing field.

Ultrasensitive Controlled Release Aptasensor Using Thymine-Hg2+-Thymine Mismatch as a Molecular Switch for Hg2+ Detection.

An ultrasensitive controlled release system electrochemical aptasensor (CRSEA) has been developed for supersensitive determination of mercury ions (Hg2+), using gold nanoparticle-linked specific single-stranded DNA (Au NPs-ssDNA) as a molecular gate and mesoporous silica nanocontainers (MSNs) as containers. MSNs have a rich porous structure, thus entrapping the toluidine blue (TB) molecules inside. It is worth noting that Hg2+ binds to the ssDNA with multiple thymine (T) and induces the ssDNA to form a hairpin structure, which makes the separation of the Au NPs-ssDNA from the MSNs. Eventually, the stored TB molecules were released from MSNs. The electron transfer signals of TB were detected stably by a differential pulse voltammetry (DPV) detection method, which are correlated with the concentration of Hg2+. Therefore, the wide linear range (10 pM-100 µM) and low limit of detection (2.9 pM) were obtained, and the system also displayed an apparent electrochemical signal response in real sample detection and showed a promising possibility in actual monitoring.