A novel flower-shaped Ag@ZIF-67 chemiluminescence sensor for sensitive detection of CEA.

In this work, a chemiluminescence (CL) aptasensor for sensitive carcinoembryonic antigen (CEA) detection was constructed based on the CL system of luminol-H2O2-NaOH. Magnetic carbon nanotubes (MCNTs), as the base material, was modified with CEA-aptamer and DNA1, and was combined with the novel flower-shaped Ag@ZIF-67 of modified with DNA2 through the principle of base complementary pairing. CEA combined with aptamer when it existed in the solution. At the same time, MCNTs was adsorbed at the bottom of the container under the influence of external magnetic field, and Ag@ZIF-67 enhanced the CL signal. The CL aptasensor demonstrated high selectivity and sensitivity for CEA in human serum sample with (1-4): a detection limit of 4.53 × 10-3 ng/mL in case the detection range was 0.05-500 ng/mL. Furthermore, the proposed method had been shown great potential in cancer diagnosis.

Electrochemical assays for determination of H2O2 and prostate-specific antigen based on a nanocomposite consisting of CeO2 nanoparticle-decorated MnO2 nanospheres.

A nanocomposite consisting of CeO2 nanoparticle-decorated MnO2 nanospheres (CeO2@MnO2) was synthesized for the first time via a hydrothermal method. CeO2@MnO2 was exploited to construct an electrochemical assays for detecting H2O2 and prostate-specific antigen (PSA) with square wave voltammetry (SWV). The electrochemical results proved that CeO2@MnO2 owned a better electrocatalytic effect towards H2O2 reduction than pure MnO2 NS and CeO2 NP due to the synergistic effect between MnO2 NS and CeO2 NP. Under optimized conditions, CeO2@MnO2-based assay can be applied to detect H2O2 in the range 1 to 3.0 × 103 µmol L-1. The label-free electrochemical immunoassay based on CeO2@MnO2 displayed linearly with concentrations of PSA from 0.005 to 50.0 ng mL-1. The electrochemical assays also possessed acceptable sensitivity, selectivity, and stability. The study showed that CeO2@MnO2 hold great potential as a biosensing platform and the clinical determination of tumor markers in human serum. Graphical abstract A nanocomposite consisting of CeO2 nanoparticles decorated MnO2 nanospheres (CeO2 @MnO2) was firstly synthesized via a hydrothermal method. CeO2@MnO2 was firstly exploited to construct electrochemical assays for detecting H2O2 and prostate-specific antigen (PSA) with square wave voltammetry (SWV), respectively. The electrochemical results proved that CeO2@MnO2 owned better electrocatalysis towards H2O2 reduction than pure MnO2 NS and CeO2 NP due to the synergistic effect between MnO2 NS and CeO2 NP. Under optimized conditions, CeO2@MnO2 based assay relative to the H2O2 system can be applied to detect H2O2 with range from 1 to 3.0 × 103 µmol L-1. The label-free electrochemical immunoassay based on CeO2@MnO2 relative to the H2O2 system displayed linearly with concentrations of PSA from 0.005 to 50.0 ng mL-1. The electrochemical assays also possessed acceptable sensitivity, selectivity and stability. The study showed that CeO2@MnO2 hold great potential for biosensing platform and the clinic determination of tumor markers in human serum.

A chemiluminescence assay for determination of lysozyme based on the use of magnetic alginate-aptamer composition and hemin@HKUST-1.

Lysozyme aptamer-functionalized magnetic alginate hydrogel was prepared for separation and enrichment of lysozyme. Luminol-labeled aptamer was used as a signal tag, and the signal tag was adsorbed on magnetic carboxylated carbon nanotubes based on the π-interaction. When lysozyme was added, the aptamer specifically binds to the lysozyme, causing the signal tag to detach from the magnetic carboxylated carbon nanotubes. When the aptamer/lysozyme complex bound to the complementary single strand of aptamer on the hemin@HKUST-1, lysozyme was released. The released lysozyme can be recombined with the signal tag adsorbed on the magnetic carboxylated carbon nanotube, allowing more signal tag to be dispersed into the solution. Determination of lysozyme was achieved by releasing the luminol-labeled aptamer to generate a chemiluminescence signal at a wavelength of 425 nm. It was proved by experiments that the synthesized hemin@HKUST-1 had a strong catalytic effect on the luminol-NaOH-H2O2 system. The chemiluminescence signal was increased nearly 100 times. The complementary pairing allowed the luminol to be immobilized on the surface of hemin@HKUST-1. The generation and consumption of short-lived reactive oxygen species were concentrated on the surface of the MOFs, which improves the chemiluminescence efficiency. The introduction of hemin@HKUST-1 and DNA solved the defects of chemiluminescence analysis. The chemiluminescence assay was able to detect lysozyme with linear range of 1.05 × 10-6 U∙mg-1 (6.00 × 10-13 mol∙L-1)-1.25 × 10-2 U∙mg-1 (7.14 × 10-9 mol∙L-1); the detection limit was 3.50 × 10-7 U∙mg-1 (2.00 × 10-13 mol∙L-1) (R2 = 0.99). The recovery of lysozyme in spiked saliva samples was 97.4-102.8%. Graphical abstract Schematic presentation of chemiluminescence assay. Lysozyme (Lys) was captured by aptamer-modified magnetic sodium alginate (M-Alg-Apt); Glycine (pH = 2) as eluent for Lys. Luminol-modified Apt (Apt-luminol) as signal tag; magnetic carbon nanotubes (MCNTs) as adsorption matrix; cDNA was complementary to Apt; hemin@HKUST-1 as catalyst.

Novel Chemiluminescence Sensor for Thrombin Detection Based on Dual-Aptamer Biorecognition and Mesoporous Silica Encapsulated with Iron Porphyrin.

Thrombin is a marker of blood-related diseases, and its detection is of great significance in the fields of medical and biological research. Herein, a novel chemiluminescence (CL) sensor for thrombin detection was prepared based on dual-aptamer biorecognition and mesoporous silica encapsulated with iron porphyrin. Mesoporous silica encapsulated with hematin by aptamer1 (Apt1/hematin/M-SiO2) and magnetic microspheres modified with aptamer2 (Apt2/NH2-MS) were successfully prepared, and the two materials were used to construct a CL sensor to detect thrombin. Primarily, Apt2/NH2-MS is used for pretreatment separation of thrombin samples by the biorecognition effect between the aptamer (Apt2) and target (thrombin). Then, thrombin/Apt2/NH2-MS is again recognized with Apt1 on the surface of Apt1/hematin/M-SiO2 and Apt1/thrombin/Apt2/NH2-MS is formed, so dual-aptamer biorecognition is realized. Meanwhile, the generated Apt1/thrombin/Apt2/NH2-MS makes Apt1 shed off the surface of M-SiO2 and release hematin. The released hematin can catalyze the luminol-H2O2 CL reaction. Therefore, a sandwich-type CL sensor was constructed based on dual-aptamer biorecognition and hematin catalysis for the detection of thrombin. The sensor has a linear range of 7.5 × 10-15 to 2.5 × 10-10 mol·L-1 and a detection limit of 2.2 × 10-15 mol·L-1 and also exhibits excellent selectivity, reproducibility, and stability. The sensor was successfully used for the detection of thrombin in serum samples, which makes it possible to apply the sensor in the detection of thrombin in actual samples.

A "signal-on" chemiluminescence biosensor for thrombin detection based on DNA functionalized magnetic sodium alginate hydrogel and metalloporphyrinic metal-organic framework nanosheets.

A "signal-on" chemiluminescence biosensor was established for detecting thrombin. The thrombin aptamer1-functionalized magnetic sodium alginate (Malg-Apt1) hydrogel was synthesized by physical interaction between sodium alginate and Ca2+, and it was used in the biosensor for separating and enriching thrombin. Ethylenediamine tetraacetic acid (EDTA) was used to chelate with Ca2+ to dissolve the hydrogel and release thrombin. A metalloporphyrinic metal-organic framework nanosheet, named as Cu-TCPP(Co) MOFs, was prepared as signal amplification strategy. Cu-TCPP(Co) MOFs/Au-ssDNA (ssDNA: single-strand DNA) was synthesized for controllable further amplification of chemiluminescent signal. The thrombin aptamer2-functionalized magnetic carbon nanotubes (MCNTs-Apt2) were used as a matrix, and Cu-TCPP(Co) MOFs/Au-ssDNA was adsorbed on the MCNTs by the complementary pairing of the partial bases between ssDNA and Apt2. Compared with ssDNA, Apt2 has a stronger interaction with thrombin. Therefore, thrombin can trigger the release of Cu-TCPP(Co) MOFs/Au-ssDNA to achieve signal amplification. Under the optimal conditions, the biosensor could detect thrombin as low as 2.178 × 10-13 mol/L with the range from 8.934 × 10-13 to 5.956 × 10-10 mol/L and exhibited excellent selectively. Moreover, the "signal-on" chemiluminescence biosensor showed potential application for the detection of thrombin in body fluids.

Enhanced electrochemiluminescence of luminol based on Cu2O-Au heterostructure enabled multiple-amplification strategy.

Herein, a credible construction strategy to improve electrochemiluminescence (ECL) of luminol was developed based on Cu2O-Au heterostructures. Summarily, gold nanoparticles (AuNPs) were anchored on surface of Cu2O nanocube (Cu2O@AuNPs) by spontaneous reduction reaction. Then, luminol molecules were concentrated on Cu2O@AuNPs using L-Cysteine (Cys) as covalent linkage to build the composite emitter (Cu2O@AuNPs-Cys-luminol). The enhancement mechanism was realized by following aspects: (I) Cu2O@AuNPs worked as electrocatalyst for glucose to generate coreactant of H2O2 in situ, avoiding the instability of direct addition of H2O2. (II) luminol molecules were firmly attached on Cu2O@AuNPs to achieve centralized and strong luminescence at low consumption. (III) Cys acted as an intramolecular coreactant and directly linked to luminol to increase luminous efficiency. To validate the effectiveness, a sandwiched immunoassay was built using concanavalinA (ConA) as analyte. Electroreduced graphene film as substrate provided phenoxy-derivatized dextran (DexP) with abundant binding sites and improved conductivity. To improve the specificity, DexP was used to identify ConA via the specific carbohydrate-ConA interaction. Then, Cu2O@AuNPs-Cys-luminol was modified on electrode as ECL signal indicator. The ECL immunosensor achieved determination of ConA with low detection limit of 2.9 × 10-5 ng/mL and excellent stability of continuous potential scan for 8 cycles. Experimental results demonstrated that the proposed construction strategy made considerable progress in ECL efficiency and stability of luminol. The creational pattern of construction strategy achieves high detection capabilities to ConA and expands the applicability of luminol in ECL system. It is expected to have more potential application value in immunoassay with universality.

Rapid fabrication of electrode for the detection of alpha fetoprotein based on MnO2 functionalized mesoporous carbon hollow sphere.

The concentration of alpha-fetoprotein (AFP) rises greatly in patients with liver cancer and it is a challenge to construct a sensitive AFP detection method with wide range. Therefore, an easy and label-free sensing electrochemical platform for AFP detection with wide concentration range had been designed in this work. Firstly, MnO2 functionalized mesoporous carbon hollow sphere (MCHS@MnO2) with optimal performance was synthesized by regulating experimental conditions and characterized by scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), etc. Then, it was immobilized on glassy carbon electrode (MCHS@MnO2/GCE) to build an immunosensor for the detection of AFP. The MCHS@MnO2/GCE can catalyze decomposition of H2O2 to generate electrochemical signal, and the signal will decrease after capturing AFP. Due to good electrocatalytic activity of MCHS@MnO2 to H2O2, the immunosensor achieved indirect detection of AFP with wide sensing range from 0.10 ng mL-1 to 420 ng mL-1 and a detection limit of 0.03 ng mL-1. Furthermore, the method had been proven to be satisfactory selectivity and reproducibility, and it was successfully applied to determine the content of AFP in human serum samples with satisfactory results. This method is expected to be used for early diagnosis and prognosis examination of liver cancer patients.

A nanocomposite prepared from bifunctionalized ionic liquid, chitosan, graphene oxide and magnetic nanoparticles for aptamer-based assay of tetracycline by chemiluminescence.

A nanocomposite was prepared from a bifunctionalized ionic liquid, chitosan on magnetic nanoparticle-modified graphene oxide (IL/Chit@MGO). It was used in a chemiluminescencc (CL) assay for tetracycline. The materials were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray powder diffraction, nitrogen adsorption-desorption isotherm, vibrating sample magnetometry and zeta potentials. Subsequently, a tetracycline-binding aptamer (TC-Apt) acting as a recognition element, and G-quadruplex DNAzyme (G-DNAzyme) acting as a signal amplification component were modified on IL/Chit@MGO. So, the bifunctional G-DNAzyme/TC-Apt/IL/Chit@MGO was prepared. The IL/Chit@MGO is found to possess excellent loading capability for TC-Apt. This is attributed to the large specific surface and abundant charge on the surface of IL/Chit@MGO. The composite was used to construct a CL assay for tetracycline. Tetracycline binds to TC-Apt and causes the release of the G-DNAzyme. The latter catalyzes the CL of luminol-H2O2 CL system at pH 7.4. Under optimized conditions, the blue CL at the emission wavelength of 425 nm increases linearly in the 0.16 pM to 2.0 nM concentration range, and the detection limit is 21 fM (at 3σ). The assay is selective, reproducible and stable. The assay was applied to tetracycline detection in practical samples. The apparent recoveries are 98.0% to 101.3% for the milk sample and 97.0% to 102.2% for the water sample. Graphical abstractG-quadruplex DNAzyme (G-DNAzyme) and tetracycline aptamer (TC-Apt) bifunctionalized ionic liquid/chitosan@magnetic graphene oxide (IL/Chit@MGO) was prepared. The nanocomposite was used to construct a chemiluminescence (CL) assay for tetracycline.

Highly selective and sensitive chemiluminescence biosensor for adenosine detection based on carbon quantum dots catalyzing luminescence released from aptamers functionalized graphene@magnetic ß-cyclodextrin polymers.

In this work, a highly selective and sensitive chemiluminescence (CL) biosensor was prepared for adenosine (AD) detection based on carbon quantum dots (CQDs) catalyzing the CL system of luminol-H2O2 under alkaline environment and CQDs was released from the surface of AD aptamers functionalized graphene @ magnetic ß-cyclodextrin polymers (GO@Fe3O4@ß-CD@A-Apt). Firstly, GO@Fe3O4@ß-CD and CQDs were prepared and characterized by transmission electron microscopy (TEM), scanning electron microscope (SEM), UV-Vis absorption spectra (UV), fluorescence spectra (FL), fourier transform infrared (FTIR) and X-ray powder diffraction (XRD). For GO@Fe3O4@ß-CD, Fe3O4 was easy to separate, GO had good biocompatibility and large specific surface area, and ß-CD further increased the specific surface area of the adenosine polymers (A-Apt) to provided larger binding sites to A-Apt. Then, A-Apt was modified on the surface of GO@Fe3O4@ß-CD while CQDs was modified by ssDNA (a single stranded DNA partially complementary to A-Apt). The immobilization property (GO@Fe3O4@ß-CD to A-Apt) and the adsorption property (GO@Fe3O4@ß-CD@A-Apt to CQDs-ssDNA) were sequentially researched. The base-supported chain-like polymers - GO@Fe3O4@ß-CD@A-Apt/CQDs-ssDNA was successfully obtained. When AD existed, CQDs-ssDNA was released from the surface of GO@Fe3O4@ß-CD@A-Apt and catalyzed CL. After that, under optimized CL conditions, AD could be measured with the linear concentration range of 5.0 × 10-13-5.0 × 10-9 mol/L and the detection limit of 2.1 × 10-13 mol/L (3δ) while the relative standard deviation (RSD) was 1.4%. Finally, the GO@Fe3O4@ß-CD@A-Apt/CQDs-ssDNA-CL biosensor was used for the determination of AD in urine samples and recoveries ranged from 98.6% to 101.0%. Those satisfactory results illustrated the proposed CL biosensor could achieve highly selective, sensitive and reliable detection of AD and revealed potential application for AD detection in monitoring and diagnosis of human cancers.

Morphology-dependent electrochemical behavior of 18-facet Cu7S4 nanocrystals based electrochemical sensing platform for hydrogen peroxide and prostate specific antigen.

18-facet polyhedron Cu7S4 nanocrystal and CuS sphere were prepared from Cu2O precursor, and CuS flower was synthesized through a simple solvothermal approach. Their electrochemical performances were investigated towards H2O2 and it was interesting to discover that Cu7S4 nanocrystal had the best electrochemical catalysis compared with CuS sphere and CuS flower. It can deduce that the special structure of Cu7S4 nanocrystal endowed it more exposed active points, higher surface area and higher Cu/S ratio. Therefore, Cu7S4 nanocrystal was firstly employed to prepare a nonenzymatic biosensor for H2O2. Satisfactory results were obtained. In addition, a label-free sensing platform for prostate specific antigen (PSA) was constructed based on electrochemical catalysis towards H2O2 of Cu7S4 nanocrystal. The label-free immunosenosr offered accurate PSA in the range of 0.001-15 ng/mL with the detection limit of 0.001 ng/mL. Besides, the immunosensor possessed good sensitivity, selectivity and stability and could detect PSA in real sample. More importantly, this work demonstrated that Cu7S4 nanocrystal hold great promising application in electrochemical sensors.

A turn-on chemiluminescence biosensor for selective and sensitive detection of adenosine based on HKUST-1 and QDs-luminol-aptamer conjugates.

In this work, HKUST-1 and QDs-luminol-aptamer conjugates were prepared. The QDs-luminol-aptamer conjugates can be adsorbed by graphene oxide through π-π conjugation. When the adenosine was added, the QDs-luminol-aptamer conjugates were released from magnetic graphene oxide (MGO), the chemiluminescent switch was turned on. It was reported that HKUST-1 can catalyze the chemiluminescence reaction of luminol-H2O2 system in an alkaline medium, and improve the chemiluminescence resonance energy transfer (CRET) between chemiluminescence and QDs indirectly. Thus, the adenosine can be detected sensitively. Based on this phenomenon, the excellent platform for detection of adenosine was established. Under the optimized conditions, the linear detection range for adenosine was 1.0 × 10-12-2.2 × 10-10 mol/L with a detection limit of 2.1 × 10-13 mol/L. The proposed method was successfully used for adenosine detection in biological samples.

Sensitive sandwich electrochemical immunosensor for alpha fetoprotein based on prussian blue modified hydroxyapatite.

A sandwich electrochemical immunosensor for the sensitive determination of alpha fetoprotein (AFP) has been fabricated. Prussian blue modified hydroxyapatite (PB@HAP) was firstly prepared and used as electrochemical label due to the wonderful conductivity and good biocompatibility of HAP. The results proved that the immunosensor fabricated using the label based on PB@HAP loaded with horse radish peroxidase (HRP) and secondary anti-AFP antibody (Ab(2)) (PB@HAP-HRP-Ab(2)) had high sensitivity, and the sensitivity of the label PB@HAP-HRP-Ab(2) was much higher than labels of PB@HAP-Ab(2), PB-HRP-Ab(2) and HAP-HRP-Ab(2). The mixture of graphene sheet (GS) and thionine (TH) was not only used to immobilize anti-AFP antibody (Ab(1)) but also took part in the signal amplification. The amperometric signal increased linearly with AFP concentration in the range of 0.02-8 ng/mL with a low detection limit of 9 pg/mL. The immunosensor had the advantages of high sensitivity, good selectivity and good stability, and was applied to the analysis of AFP in serum sample with satisfactory results. Due to the low-cost and easy synthesis of PB@HAP, the screen-printed electrodes could be used instead of the bare glass carbon electrode in order to achieve mass production. In addition, it had potential application in the detection of other tumor markers.

A novel chemiluminescent flow-injection analysis of transferrin by its reduction of the luminol--hydrogen peroxide reaction catalysed by meso-tetra-(3-methoxyl-4-hydroxyl) phenyl manganese porphyrin.

Based on the inhibition effect of transferrin (Tf) on the reaction of the luminol-hydrogen peroxide (H(2)O(2)) chemiluminescence (CL) system, catalysed by meso-tetra-(3-methoxyl-4-hydroxyl) phenyl manganese porphyrin (MnP) as a mimetic enzyme of peroxides, a sensitive flow-injection CL method has been developed for the determination of Tf in an alkaline medium. The CL reaction was carefully investigated by examining the variations of reaction conditions. Under optimum conditions, the linear range for the determination of transferrin was 0.04-20.0 µg/mL and the detection limit was 1.62 ng/mL. This proposed method was sensitive, convenient and simple, and has been successfully applied to the determination of transferrin in a serum sample.

Ultrasensitive electrochemical immunoassay for BRCA1 using BMIM·BF4-coated SBA-15 as labels and functionalized graphene as enhancer.

BRCAl is an anti-oncogene in women, who are genetically predisposed to breast and ovary cancer. The detection of BRCA1 can offer an opportunity to characterize the function of genetic features in breast and ovarian cancer and to screen breast or ovarian cancer patients. In this study, we designed a new label and fabricated a novel sandwich-type electrochemical immunoassay for the ultrasensitive detection of BRCAl. Horseradish peroxidase (HRP) was entrapped in the pores of amino-group functionalized SBA-15 and the secondary antibody (Ab2) combined with SBA-15 by covalent bond. Ionic liquid (IL) was added into the mixed solution of SBA-15/HRP/Ab2 and application of IL increased the electrochemical activity of HRP and promoted electron transport. The synergistic effect between IL, SBA-15, Ab2 and HRP could retain the bioactivity of HRP and Ab2. The sensitivity of the sandwich-type immunosensor using SBA-15/HRP/Ab2/BMIM·BF4 as labels for BRCA1 detection was much higher than that using either SBA-15/HRP/Ab2 or SBA-15/Ab2 as labels. Under optimal conditions, the electrochemical immunoassay exhibited a wide working range from 0.01 to 15 ng/mL with a detection limit of 4.86 pg/mL BRCA1. The precision, reproducibility, and stability of the immunoassay were acceptable.