Study On The Application Of Metal And Functionalized Carbon Nanomaterials In Biosensors

With the rapid development of nano-science and technology, the preperation of nanomaterials become more and more perfect, many kinds of nanomaterials have been widely used for constructing the biosensor. Electrochemiluminescence (ECL) biosensors is a novel biosensors which combine electrochemiluminescence technology and bioanalytical method together with ECL luminophores as the indicator and the biologically active element (e.g. tissue, cell receptors, antibodies, enzymes, nucleic acids, etc.) as the sensitive recognize elment. Due to the unique optical, electronic, magnetic and catalytic properties, nanomaterials gain a great deal of attention. This article adopt new signal amplification strategy and nanomaterials such as Pt nanoparticles, Au nanoparticles,, multi-walled carbon nanotubes, manganese dioxide-graphene composite to construct a series of excellent performed sandwich immunosensors. The detailed contents are described as follows:1. An ultrasensitive electrochemiluminescence immunoassay based on supersandwich DNA structure amplification with histidine as a co-reactantHere we report a novel electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of carcinoembryonic antigen (CEA) via histidine labeled supersandwich DNA structure to amplify the ECL signal. Histidine is an α-amino acid with an imidazole group, which can act as a co-reactant of tris(2,2’-bipyridyl) ruthenium(Ⅱ) (Ru(bpy)32+) to amplify ECL signal. To the best of our knowledge, this is the first time to use histidine as co-reactant of Ru(bpy)32+ for signal amplification. The ECL substrate is fabricated by locating the complex of Pt nanoparticles (PtNPs) and Ru(bpy)32+(Ru-PtNPs) on Nafion modified electrode surface. In the presence of antigens, the sandwiched immunocomplex can be formed between the primary antibodies on the ECL substrate and the secondary antibodies on the gold nanoparticles. The carried auxiliary probe Ⅰ trigger a cascade of hybridization events between alternating auxiliary probe Ⅰ and histidine-modified auxiliary probe Ⅱ to form the long DNA concatamers. Thus the long DNA concatamers contain multiple histidine-modified auxiliary probe Ⅱ, which accordingly achieve significant signal amplification. As a result, the sensitivity of proposed immunosensor for CEA detection is improved, the linear range is from 0.1 pg/mL to 100 ng/mL with a low detection limit of 33.3 fg/mL.2. A supersandwich electrochemiluminescence immunosensor based on mimic-intramolecular interaction for sensitive detection of proteinsAn electrochemiluminescence (ECL) immunoassay protocol was developed based on mimicintramolecular interaction for sensitive detection of prostate specific antigen (PSA). It was constructed by integrating the ECL luminophore (tris(4,4’-dicarboxylicacid-2,2’-bipyridyl)-ruthenium(Ⅱ)dichloride (Ru(dcbpy)32+)) and coreactant (Histidine) into the supersandwich DNA structure. This strategy was more effective in amplifying the ECL signal by shortening the electronic transmission distance, improving the ECL luminous stability and enhancing the ECL luminous efficiency. The ECL matrices denoted as MWCNTs@PDA-AuNPs were fabricated through spontaneous oxidative polymerization of dopamine (DA) on multiwalled carbon nanotubes (MWCNTs) and reducing HAuCl4 to produce gold nanoparticles (AuNPs) by DA simultaneously. Then, the prepared matrices were applied to bind capture antibodies. Moreover, supersandwich Ab2 bioconjugate was designed using a PAMAM dendrimer to immobilize the detection antibody and supersandwich DNA structure. The PAMAM dendrimer, with a plurality of secondary and tertiary amine groups, not only facilitated high-density immobilization of the detection antibody and supersandwich DNA structure, but also greatly amplified the ECL signal of Ru(dcbpy)32+. The supersandwich DNA structure contained multiple Ru(dcbpy)32+ and histidine, further amplifying the ECL signal. The proposed supersandwich immunosensor showed high sensitivity with a detection limit of 4.2 fg/mL and a wide linear range of 0.01 pg/mL to 40.00 ng/mL.3. A signal-on electrochemiluminescence aptasensor based on the quenching effect of manganese dioxide for sensitive detection of carcinoembryonic antigenWe developed a signal-on electrochemiluminescence (ECL) aptasensor by using SI-ATRP to facilitate highdensity immobilization of luminophores and manganese dioxide-graphene (MnO2-GO) composite to indirect deactivate the excited state of Ru(dcbpy)32+ for ultrasensitive detection of carcinoembryonic antigen (CEA). In this approach, manganese dioxide-graphene (MnO2-GO) composite served as an efficient quencher for indirect deactivating the excited state of Ru(dcbpy)32 Surface initiated atom transfer radical polymerization (SI-ATRP) was applied to functionalize multiwalled carbon nanotubes (MWNTs) with glycidyl methacrylate (GMA) as the functional monomer. A nanocomposite material of polyamidoamine (PAMAM) dendrimer encapsulated AuNPs was used as the carrier to combine Ru(dcbpy)32+ and poly-GMA together for the synthesis of the ECL matrices. The prepared matrices were applied to bind amino-modified auxiliary probe I (Ai), which was partially complementary with the CEA aptamer. Meanwhile, the MnO2-GO composite was modified with another amino-modified CEA aptamer-partial-complementary auxiliary probe Ⅱ (A2). Through the hybridization of CEA aptamer with A1 and A2, the quencher MnO2-GO composite was linked with the ECL matrices, by which a low ECL signal was detected (off-state). However, in the presence of CEA, the sandwich-like structure was destroyed because CEA would bind to its aptamer in lieu of the auxiliary probes, which resulted in a recovery of ECL signal (on-state). The proposed ECL aptasensor showed high sensitivity with a detection limit of 25.3 fg/mL and a wide linear range of 0.1 pg/mL to 20 ng/mL.