Cucurbituril and Azide Cofunctionalized Graphene Oxide for Ultrasensitive Electro-Click Biosensing

"Click" Chemistry for the Functionalization of Graphene Oxide with Phosphorus Dendrons: Synthesis, Characterization and Preliminary Biological Properties

Two families of phosphorhydrazone dendrons having either an azide or an alkyne linked to the core and diverse types of pyridine derivatives as terminal functions have been synthesized and characterized. These dendrons were grafted via click reaction to graphene oxide (GO) functionalized with either alkyne or azide functions, respectively. The resulting modified-GO and GO-dendrons materials have been characterized by Fourier Transform Infrared (FTIR), Raman spectroscopy (RS), and Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) analyses. In addition, the free dendrons and the dendrons grafted to GO were tested toward cancerous (HCT116) and non-cancerous (RPE1) cell lines.

Enrichment and detection of VEGF165 in blood samples on a microfluidic chip integrated with multifunctional units

In this paper, a multifunctional microfluidic chip integrated with a centrifugal separation zone, aqueous two-phase system (ATPS) mixing zone and enrichment detection zone was proposed and fabricated. An automatic and efficient separation and quantitative analysis method for vascular endothelial growth factor 165 (VEGF₁₆₅) in whole blood samples was established with the designed microfluidic chip. A blood sample was divided into blood cells and plasma in the centrifugation zone. In the ATPS mixing zone, plasma was mixed with PEG/KH₂PO₄ aqueous two-phase solution containing Apt-Au NP nanoprobes. In the enrichment detection zone, the mixture was separated on CN140 modified with a ZnO NP-anti VEGF₁₆₅ nanostructure. The VEGF₁₆₅ captured by Apt-Au NPs was distributed in the PEG phase, concentrated at the front of CN140 and combined with anti-VEGF₁₆₅ to form a sandwich structure. The sensitive detection of VEGF₁₆₅ was achieved through fluorescence resonance energy transfer between rhodamine B and Au NPs on the nanoprobe. Under the optimized rotation program, capillary and centrifugal forces propelled the fluid in the whole process of pretreatment and detection. The detection linear range was between 1 pg mL^-1 and 50 ng mL^-1, the detection limit of VEGF₁₆₅ in blood was 0.22 pg mL^-1 and the enrichment efficiency was 983. It was illustrated that a convenient and reliable way for detection of tumor markers based on the multifunctional microfluidic chip was provided and it has a potential value for early screening and prognosis of clinical cancer.

A novel electrochemical aptasensor for exosomes determination and release based on specific host-guest interactions between cucurbit [7]uril and ferrocene

The superior supramolecular recognition ability of macrocyclic compounds will enhance the sensitivity and selectivity of electrochemical detection, which has a great application potential in electrochemical sensing. Herein, we developed a novel electrochemical aptasensor based on the specific host-guest interactions between cucurbit [7]uril and ferrocene (Fc) for capture, determination and release of exosomes. Macrocyclic compounds, cucurbit [7]uril is modified on the surface of the gold nanoparticles composed electrode by self-assembling. CD63 aptamer linked ferrocene is introduced into this platform to capture exosomes specifically by CD63 protein on the exosomes. The dual specificity of macrocyclic compounds and aptamers enables highly selective and sensitive electrochemical detection of exosomes. The limit of detection (LOD) was 482 particles μL^-1. In addition, the captured exosomes could be released on demand in a very mild manner through aminoferrocene (NH₂-Fc) because of its higher affinity to cucurbit [7]uril. The proposed electrochemical aptasensor showed good performance in detecting exosomes even in plasma samples, thus demonstrating its great potential in early clinical diagnosis. Simultaneously, exosomes could be released undamaged by this protocol, exhibiting good applicability in comprehensive studies of exosomes. Moreover, this strategy can be applied to other target biomolecules by changing the recognition pairs.

Bioinspired Artificial "Clickase" for the Catalytic Click Immunoassay of Foodborne Pathogens

The copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction has drawn increasing attention in the field of analytical science. However, the poor stability of Cu(I) usually hinders not only the simplicity of the click reaction but also its applications in precise analyses. Therefore, the development of a nanocatalyst containing stable Cu(I) is of great significance for broadening the application of CuAAC-based assays. Herein, inspired by the active center structure of natural multicopper oxidases (MCOs), we successfully prepared a novel nanocatalyst containing abundant stable Cu(I) as an artificial "clickase" (namely, CCN) by using glutathione to stabilize Cu(I). The stability and enzyme-like catalytic activity in the CuAAC reaction of the prepared CCN clickase were studied, and the catalytic mechanism of the CCN clickase-mediated CuAAC reaction between 3-azide-7-hydroxycoumarin (Azide 1) and propargyl alcohol (Alkyne 2) was also revealed. Compared with the existing solid CuO nanocatalysts used in CuAAC-based assays, CCN clickases exhibited plenty of superior properties (including high stability, excellent catalytic activity, no requirements of dissolution and reducing agents/radical initiator during the detection, well-defined porosities benefiting the substrate diffusion, and good biocompatibility), which can greatly increase the reaction efficiency and shorten the detection time. Encouraged by these remarkable performances, CCN clickases were used as labels to establish a new catalytic click fluorescence immunoassay for foodborne pathogens. Notably, the proposed CCN clickase-based immunoassay exhibited high analytical performances for the quantification of Salmonella enteritidis in the linear range of 10²-10⁶ CFU/mL with a limit of detection as low as 11 CFU/mL. The developed method has also been used in the determination of S. enteritidis in food samples, showing its great potential in the detection of foodborne pathogens.

Design Strategies for Electrochemical Aptasensors for Cancer Diagnostic Devices

Improved outcomes for many types of cancer achieved during recent years is due, among other factors, to the earlier detection of tumours and the greater availability of screening tests. With this, non-invasive, fast and accurate diagnostic devices for cancer diagnosis strongly improve the quality of healthcare by delivering screening results in the most cost-effective and safe way. Biosensors for cancer diagnostics exploiting aptamers offer several important advantages over traditional antibodies-based assays, such as the in-vitro aptamer production, their inexpensive and easy chemical synthesis and modification, and excellent thermal stability. On the other hand, electrochemical biosensing approaches allow sensitive, accurate and inexpensive way of sensing, due to the rapid detection with lower costs, smaller equipment size and lower power requirements. This review presents an up-to-date assessment of the recent design strategies and analytical performance of the electrochemical aptamer-based biosensors for cancer diagnosis and their future perspectives in cancer diagnostics.

Highly sensitive detection of carcinoembryonic antigen using copper-free click chemistry on the surface of azide cofunctionalized graphene oxide

In this study, we reported a highly sensitive method for detecting carcinoembryonic antigen (CEA) based on an azide cofunctionalized graphene oxide (GO-N₃) and carbon dot (CDs) biosensor system. Carbon dots-labeled DNA (CDs-DNA) combined with GO-N₃ using copper-free click chemistry (CFCC), which quenched the fluorescence of the CDs via fluorescence resonance energy transfer (FRET). Upon the addition of CEA, fluorescence was recovered due to the combination of CEA and aptamer. Under optimal conditions, the relative fluorescence intensity was linear with CEA concentration in the range of 0.01-1 ng/mL (R² = 0.9788), and the limit of detection (LOD) was 7.32 pg/mL (S/N = 3). This biosensor had a high sensitivity and good selectivity for CEA detection in serum samples, indicating that the novel sensor platform holds a great potential for CEA and other biomarkers in practical applications.

Cucurbit[8]uril-Derived Graphene Hydrogels

The scalable production of uniformly distributed graphene (GR)-based composite materials remains a sizable challenge. While GR-polymer nanocomposites can be manufactured at a large scale, processing limitations result in poor control over the homogeneity of hydrophobic GR sheets in the matrices. Such processes often result in difficulties controlling stability and avoiding aggregation, therefore eliminating benefits that might have otherwise arisen from the nanoscopic dimensions of GR. Here, we report an exfoliated and stabilized GR dispersion in water. Cucurbit[8]uril (CB[8])-mediated host-guest chemistry was used to obtain supramolecular hydrogels consisting of uniformly distributed GR and guest-functionalized macromolecules. The obtained GR hydrogels show superior bioelectrical properties over identical systems produced without CB[8]. Utilizing such supramolecular interactions with biologically derived macromolecules is a promising approach to stabilize graphene in water and avoid oxidative chemistry.

Copper(I)-Catalyzed Click Chemistry as a Tool for the Functionalization of Nanomaterials and the Preparation of Electrochemical (Bio)Sensors

Proper functionalization of electrode surfaces and/or nanomaterials plays a crucial role in the preparation of electrochemical (bio)sensors and their resulting performance. In this context, copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) has been demonstrated to be a powerful strategy due to the high yields achieved, absence of by-products and moderate conditions required both in aqueous medium and under physiological conditions. This particular chemistry offers great potential to functionalize a wide variety of electrode surfaces, nanomaterials, metallophthalocyanines (MPcs) and polymers, thus providing electrochemical platforms with improved electrocatalytic ability and allowing the stable, reproducible and functional integration of a wide range of nanomaterials and/or different biomolecules (enzymes, antibodies, nucleic acids and peptides). Considering the rapid progress in the field, and the potential of this technology, this review paper outlines the unique features imparted by this particular reaction in the development of electrochemical sensors through the discussion of representative examples of the methods mainly reported over the last five years. Special attention has been paid to electrochemical (bio)sensors prepared using nanomaterials and applied to the determination of relevant analytes at different molecular levels. Current challenges and future directions in this field are also briefly pointed out.

Electrochemiluminescence response of a benzouril-constructed electrode to bipyridyl herbicides

An electrochemiluminescence sensor with modification of macrocyclic benzo[6]uril on the surface of a glass carbon electrode was achieved, which has been applied for the quantitative analysis of paraquat and diquat.

Dual-Wavelength Ratiometric Electrochemiluminescence Immunosensor for Cardiac Troponin I Detection

Ratiometric electrochemiluminescence (ECL) has attracted special focus in the biological analysis field, because it could eliminate the environmental interference and allow for precise measurement. Herein, a dual-wavelength ratiometric ECL biosensor was designed for the detection of cardiac troponin I (cTnI), where (4,4'-dicarboxylic acid-2,2'-bipyridyl) ruthenium(II) (Ru(dcbpy)₃²⁺) and Au nanoparticle-loaded graphene oxide/polyethylenimine (GPRu-Au) nanomaterial acts as an acceptor, and Au nanoparticle-modified graphitic phase carbon nitride nanosheet composite (Au-CNN) acts as donor. Au-CNN shows a high and steady ECL signal centered at 455 nm, which is well-matched with the adsorption of GPRu-Au; thereby, a highly efficient electrochemiluminescent resonance energy transfer (ECL-RET) sensing platform is designed. AuNPs facilitate the immobilization of antibody on the nanomaterials through a Au-N bond. The high surface area of graphene oxide/polyethylenimine allows a large number of Ru(dcbpy)₃²⁺ to be loaded, immensely amplifying the ECL signal. This sensing platform exhibits outstanding analytical performance toward cTnI with a detection limit of 3.94 fg/mL (S/N = 3). The high reliability, selectivity, and sensitivity of this ratiometric ECL biosensor provides a versatile sensing platform for the bioanalysis.

Electrochemical Assay of the Alpha Fetoprotein-L3 Isoform Ratio To Improve the Diagnostic Accuracy of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is now the major malignant disease with high morbidity and mortality, which seriously endangers human lives and health. Alpha fetoprotein (AFP) assay is a commonly used serological biomarker for clinical diagnosis of HCC, but it lacks specificity. Analysis of its isoform AFP-L3, especially the AFP-L3 ratio in total AFP (AFP-L3%), can significantly improve the specificity for HCC identification. Herein, an electrochemical approach has been first proposed for simple, accurate, and fast determination of AFP-L3% in clinical samples. On the basis of two independent electrochemical signals generated from the synthesized nanoparticles, 4-mercaptophenylboronic acid (MPA)-functionalized copper nanoparticles (MPA-CuNPs) and the Lens culinaris agglutinin (LCA)-functionalized silver nanoparticles (LCA-AgNPs), simultaneous quantification of the AFP-L3 and total AFP in serum sample has been achieved, thus achieving directly the electrochemical assay of AFP-L3%. To be noted, both the assay time and the assay procedure have been significantly compressed when compared to that of available techniques in clinical use. Therefore, with the integration of electrochemical techniques, this new approach for AFP-L3% analysis would be promising for the accurate diagnosis of HCC.