| As a high-tech interdiscipline, nanotechnology which appeared in the late20th century covers diverse fields, including chemistry, biology, materials science and physics. Nanomaterials exhibit a wide range of applications in many areas because of their special advantages, such as small size effect, interface effect and quantum effect. In recent years, with the development of nanotechnology, functional nanocomposites showed a huge advantage in some special research topics. These materials not only maintain the special nature of nanomaterials, but also possess superior electrical and optical characteristics of nanocomposites.Aptamer is specific DNA or RNA strand obtained from random-sequence nucleic acid libraries by SELEX technology. Compared with antibodies, aptamer has distinct advantages such as high bioaffinity, easy synthesis, high specificity and good stability. For the past several years, aptamer as recognition element has aroused more and more interest in the biomedical science, drug delivery, molecular imprinting and clinical diagnostics.Electrochemiluminescence (ECL), a light emission motivated by the high-energy electron transfer reaction, has become a powerful analytical tool for highly sensitive and specific detection of real samples due to its high sensitivity, high selectivity, excellentlytemporal and spatial controllability. Nowadays, the ECL technique has been extensively used in the areas of immunoassay, drug monitoring, clinical diagnosis, food and watertesting.1. A novel label-free electrochemiluminescence (ECL) aptasensor for sensitive and selective detection of thrombin was constructed using Ru(bpy)32+functionalized dopamine-melanin colloidal nanospheres (Dpa-melanin CNSs) and gold nanoparticles (AuNPs) as signal-amplifying tags. Dpa-melanin CNSs were synthesized by a simple chemical route. A large amount of Ru(bpy)32+was coated over the Dpa-melanin CNSs with large surface area using Nafion as a bridge to form the Ru(bpy)32+/Nafion/Dpa-melanin CNSs composite which was considered as a sensing platform. AuNPs were introduced to the platform for immobilization of aptamer and further amplification of signal. A label-free ECL aptasensor for thrombin detection was subsequently fabricated by assembling aptamer on AuNPs/Ru(bpy)32+/Nafion/Dpamelanin CNSs modified electrode. Greatly enhanced sensitivity is achieved based on the dual signal amplification strategy. The high sensitive detection of thrombin could be realized and the detection limit of thrombin was down to2.2×10-13mol L-1with a linear range from1.0×10-12to1.0×10-9mol L-1. The aptasensor was applied to the thrombin analysis of human plasma samples with recoveries of86.0-97.7%.2. A label-free competitive ECL aptasensor for the determination of17P-estradiol (E2) was developed based on gold electrode with enhanced detection sensitivity. Construction of the aptasensor began with immobilizing the thiol-capped E2aptamer onto the gold electrode. A designed complementary DNA (cDNA) was employed as a detection probe to bind with the unbound E2aptamer. The presence of cDNA could absorb more Ru(bpy)32+, making the ECL intensity greatly enhanced. When the aptamer captured E2, the binding of cDNA to the aptamer was inhibited, the decrease in the electrode response was observed. On the basis of the present strategy, the competitive aptasensor based on the specific binding of E2aptamer to E2and cDNA was achieved. The biosensor for E2possess widely linear detection range from0.01to10nmol L-1with a detection limit of1.1×10-12mol L-1(S/N=3). The application of the present protocol was demonstrated by analyzing E2in human serum, human urine and tap water samples with the recoveries of89.8-100.0%,90.0-103.5%and89.5-95.0%respectively. The proposed method provides a powerful tool for the rapid and sensitive detection of small molecules in biological and environmental samples. 3. A sandwich-type luminol ECL aptasensor for highly sensitive and selective detection of platelet-derived growth factor BB (PDGF-BB) is fabricated. For this proposed ECL aptasensor, a multilayered AuNPs-electrochemically reduced graphene (AuNPs-EG) nanocomposite film was formed on the GCE surface as the base of the aptasensor through a co-electrodeposition method. The AuNPs-EG composites possess high conductivity to promote the electron transfer at the electrode interface and good biocompatibility and large surface area to capture large amounts of primary aptamer (Apt1), thus amplifying the detection response. Moreover, glucose oxidase (GOD) functionalized AuNPs labeled secondary aptamer (GOD-Apt2-AuNPs) was designed as the signal probe for the sandwiched aptasensor. Enhanced sensitivity was obtained by in situ generating H2O2from reaction between GOD and glucose and the excellent catalytic behavior of AuNPs to the ECL of luminol-H2O2system. Under the optimal conditions, the as-prepared ECL aptasensor exhibited excellent analytical property for the detection of PDGF-BB in the range from1.0×10-13to5.0×10-10mol L-1with a detection limit of1.7×10-14mol L-1(S/N=3). The application of the present protocol was demonstrated by analyzing PDGF-BB in human serum and human urine samples with the recoveries from85.0%to110%.4. This work describes a novel ECL aptasensor for highly sensitive detection of PDGF-BB using aptamer functionalized CdS quantum dots-polyamidoamine as probe (CdS QDs-PAMAM-Apt). CdS QDs-PAMAM nanocomposites were synthesized by one-pot synthesis in methanol. The prepared nanocomposites were linked with the NH2-aptamer2(Apt2) of PDGF-BB to form the CdS QDs-PAMAM-Apt2probe by glutaraldehyde as coupling reagent. For constructing the aptasensor, MWCNTs-chitosan composites and NH2-aptamer1(Aptl) with the same base sequence as Apt2were immobilized on the electrode by self-assembled method to recognize the target protein PDGF-BB. In the presence of PDGF-BB, the structure of sandwiched format was formed between the Aptl and the CdS QDs-PAMAM-Apt2probe, thereby resulting in a proportional increase of ECL emission. Thanks to the significant enhancement of high loading of CdS QDs by the PAMAM dendrimer and the advantage of MWCNTs for accelerating the electron transfer, the highly sensitive detection of PDGF-BB with a detection limit of0.13pmol L-1was achieved. The linear range is from0.5pmol L-1to1nmol L-1. The present protocol was applied to the analysis of PDGF-BB in human serum samples. The recoveries of PDGF-BB in human serum samples are87.2-113%.5. A novel ECL aptasensor based on the flowerlike CdS-C composites was designed for the detection of carcinoembryonic antigen (CEA). CdS-C composites were immobilized on the glassy carbon electrode surface as ECL emitter attached a capture aptamer (NH2-Apt) of CEA. Au nanorod functioned with cDNA and DNAzyme was employed as detection probe. DNAzyme has horseradish peroxidase-like activity and could electrocatalyze the reduction of H2O2, leading to an obvious ECL quenching. In the presence of CEA, it conjugated with capture probe and thereafter the detection probe released, which decreased the consumption of H2O2, producing an increased ECL signal, the as-prepared ECL aptasensor exhibited excellent analytical property for the detection of CEA in the range from1.0×10-13to5.0×10-10g mL-1with a detection limit of3.6×10-14g mL-1(S/N=3). The prepared aptasensor has been applied to determination of CEA in human serum samples. The recoveries of CEA in human serum samples are88.2-106%. |
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