Feifei Lan

Applications of graphene and related nanomaterials in analytical chemistry

Graphene has emerged as a rapidly rising star in the field of materials science since its successful preparation in 2004. Due to its distinguished electrical, chemical and optical performances, graphene and its derivatives have also generated huge interest in analytical chemistry. This article critically and comprehensively reviews the emerging graphene-based electrochemical analysis, photochemical analysis and extraction. We present a review of the current literature concerning the electrochemical applications and advancements of graphene in the detection of metal ions, gases, nucleic acids, proteins, cells, bacteria and other molecules. Meanwhile, we summarize the application of graphene in photoanalysis (including graphene-based fluorescence resonance energy transfer sensors and optical sensors). In addition, we comment on the application and advantages of graphene in extraction. We emphasize the unique roles and advantages of graphene materials used in analytical chemistry.

Microfluidic paper-based analytical device for photoelectrochemical immunoassay with multiplex signal amplification using multibranched hybridization chain reaction and PdAu enzyme mimetics

Combining multibranched hybridization chain reaction (mHCR), the photoelectrochemical (PEC) immunosensor was fabricated with a microfluidic paper-based analytical devices using different sizes of CdTe quantum dots (QDs) sensitized flower-like 3D ZnO superstructures as photoactive materials. Firstly, 4-aminothiophenol (PATP) functioned ZnO was anchored on gold-paper working electrode. With the aid of PATP, large-sized CdTe-COOH QDs (QDs1) were conjugated onto the ZnO surface because of the formation of a strong bond (Zn-S) between the thiol of PATP molecule and the ZnO, and the remaining amino group formed an amide bond with carboxylic acid group capping CdTe. Then the small-sized CdTe-NH2 QDs (QDs2) were modified on the QDs1 by forming amide bond, which leaded to a very strong photocurrent response because of the formation of cosensitized structure. The designed mHCR produced long products with multiple branched arms, which could attached multiple PdAu nanoparticles and catalyze the oxidation of hydroquinone (HQ) using H2O2 as anoxidant. Double strands DNA with multiple branched arms (mdsDNA) was formed by mHCR. In the presence of carcinoembryonic antigen (CEA), PdAu-mdsDNA conjugates-labeled CEA antibody was captured. The concentrations of CEA were measured through the decrease in photocurrent intensity resulting from the increase in steric hindrance of the immunocomplex and the polymeric oxidation product of HQ. In addition, the oxidation product of HQ deposited on the as-obtained electrode, which could efficiently inhibit the photoinduced electron transfer. Under optimal conditions, the PEC immunosensor exhibited excellent analytical performance: the detection range of CEA was from 0.001 to 90 ng mL(-1) with low detection limit of 0.33 pg mL(-1). The as-obtained immunosensor exhibited excellent precision, prominent specificity, acceptable stability and reproducibility, and could be used for the detection of CEA in real samples. The proposed assay opens a promising platform of clinical immunoassay for other biomolecules.

Ultrasensitive Photoelectrochemical Biosensing of Cell Surface N-Glycan Expression Based on the Enhancement of Nanogold-Assembled Mesoporous Silica Amplified by Graphene Quantum Dots and Hybridization Chain Reaction

An ultrasensitive photoelectrochemical (PEC) biosensor for N-glycan expression based on the enhancement of nanogold-assembled mesoporous silica nanoparticles (GMSNs) was fabricated, which also combined with multibranched hybridization chain reaction (mHCR) and graphene quantum dots (GQDs). In this work, the localized surface plasmon resonance, mHCR and GQDs-induced signal amplification strategies were integrated exquisitely and applied sufficiently. In the fabrication, after porous ZnO spheres immobilized on the Au nanorod-modified paper working electrode were sensitized by CdTe QDs, the GMSNs were assembled on the CdTe QDs. Then the photocurrent efficiency was improved by the sensitization of the CdTe QDs and the localized surface plasmon resonance of GMSNs. Successively, the products of mHCR with multiple biotins for multiple horseradish peroxidase binding and multiple branched arms for capturing the target cells were attached on the as-prepared electrode. The chemiluminescent (CL) emission with the aid of horseradish peroxidase served as an inner light source to excite photoactive materials for simplifying the instrument. Furthermore, the aptamer could capture the cancer cells by its highly efficient cell recognition ability, which avoided the conventional routing cell counting procedures. Meanwhile, the GQDs served as the signal amplication strategy, which was exerted in the process of N-glycan evaluation because the competitive absorption of exciting light and consumption of H2O2 served as the electron donor of the PEC system and the oxidant of the luminol-based CL system. This judiciously engineered biosensor offered a promising platform for the exploration of N-glycan-based physiological processes.

Fluorescence "turn-on" determination of H2O2 using multilayer porous SiO2/NGQDs and PdAu mimetics enzymatic/oxidative cleavage of single-stranded DNA.

A 3D microfluidic paper-based fluorescence analytical device with hollow channels based on the turn-on switching of a resonance energy transfer triggered by the •OH induced cleavage of a DNA strand was successfully constructed. And this fluorescent nanoplatform was first designed to achieve in situ and real-time determination of H2O2 released from cancer cells to obtain an accurate determination. With optimal conditions, the proposed method displayed excellent analytical performance for the detection of H2O2 ranging from 0.3 to 1.0mM with a detection limit of 0.1nM. The favorable performances of this sensor were due to the peroxidase-like activity of nitrogen-doped graphene quantum dots (multilayer porous SiO2 act as stabilizer to load more nitrogen-doped graphene quantum dots for signal amplification) and folic acid-pPdAu/GO (which also could act as an efficient fluorescence quencher and a recognition element of cancer cells by folic acid). It was worth noting that it could be used for visually determined the flux of H2O2 from the cells. Therefore, the developed biosensor holds potential for ultrasensitive quantitative analysis of H2O2 and supplies valuable information for diabetes mellitus research and clinical diagnosis.

Ultrasensitive electrochemiluminescence assay of tumor cells and evaluation of H 2 O 2 on a paper-based closed-bipolar electrode by in-situ hybridization chain reaction amplification

In this manuscript, a disposable paper-based analytical device comprised of a closed bipolar electrode (BPE) was fabricated for the ultrasensitive electrochemiluminescence (ECL) detection of intracellular H2O2 and the number of cancer cells. In this approach, wax printing was used to fabricated reaction zone, and carbon ink-based BPE and driving electrodes were screen-printed into the paper. AuPd nanoparticles (NPs), which served as a carrier of the capture aptamer and as the catalyst for the ECL reaction of luminol and H2O2, were used to modify the BPE. Luminol/Au NPs were attached to the surface of the captured cells via hybridation chain reaction with two hairpin structure DNA labelled luminol/Au NPs. In the stimulation of phorbol myristate acetate, The coreactant H2O2 was released from the target cells. The ECL response of the luminol-H2O2 system was related to the number of cancer cells in the testing buffer, which served as a quantitative signal for the determination of cancer cells and the concentration of H2O2. In order to decrease the external voltage, K3[Fe(CN)6] was introduced in the cathode resevoir of BPE because it gained electrons at the cathode more easily than oxygen. The ECL intensity was quantitatively related to the concentration of MCF-7 in the range of 1.0 × 102-1.0 × 107 cells/mL. The detection limit was 40 cells/mL and it showed good specificity for cells with high overexpression of mucin-1 receptor, it was concluded that the developed protocol could be effectively utilized for the detection of MCF-7 cells.

Paper analytical devices for dynamic evaluation of cell surface N-glycan expression via a bimodal biosensor based on multibranched hybridization chain reaction amplification.

A novel colorimetric/fluorescence bimodal lab-on-paper cyto-device was fabricated based on concanavalin A (Con A)-integrating multibranched hybridization chain reaction (mHCR). The product of mHCR was modified PtCu nanochains (colorimetric signal label) and graphene quantum dot (fluorescence signal label) for in situ and dynamically evaluating cell surface N-glycan expression. In this strategy, preliminary detection was carried out through colorimetric method, if needed, then the fluorescence method was applied for a precise determination. Au-Ag-paper devices increased the surface areas and active sites for immobilizing larger amount of aptamers, and then specifically and efficiently captured more cancer cells. Moreover, it could effectively reduce the paper background fluorescence. Due to the specific recognition of Con A with mannose and the effective signal amplification of mHCR, the proposed strategy exhibited excellent high sensitivity for the cytosensing of MCF-7 cells ranging from 100 to 1.0×10(7) and 80-5.0×10(7) cellsmL(-1) with the detection limit of 33 and 26 cellsmL(-1) for colorimetric and fluorescence, respectively. More importantly, this strategy was successfully applied to dynamically monitor cell-surface multi-glycans expression on living cells under external stimuli of inhibitors as well as for N-glycan expression inhibitor screening. These results implied that this biosensor has potential in studying complex native glycan-related biological processes and elucidating the N-glycan-related diseases in biological and physiological processes.

Sudoku-like Lab-on-Paper Cyto-Device with Dual Enhancement of Electrochemiluminescence Intermediates Strategy

This paper describes the design and construction of a sudoku-like lab-on-paper platform, in which dual enhancement of reaction intermediates strategy was incorporated for multiplexed competitive electrochemiluminescence (ECL) cyto-assay. Benefiting from the sudoku-like structure, integrated multifunctions were obtained on such an elaborately devised platform, including specific reagents storage, multiple samples immobilization, residual automatic washing, and signal collection. By utilizing semicarbazide (SE) and silver nanoparticles (AgNPs) as dual enhancers, more ECL intermediates could be obtained in the graphene quantum dots (GQDs) and peroxydisulfate system, resulting in the production of more excited-state GQDs to emit light. Moreover, the double-stranded DNA nanowire with multiple branched arms (MBdsDNA) was chosen as an efficient nanocarrier to load more GQDs and AgNPs. Via immobilizing AgNPs on the end of the plentiful branched arms, Ag-MBdsDNA were obtained and trapped on the sensing interface through the valid competitive interactions between target cells and Ag-MBdsDNA. Afterward, abundant GQDs were attached to the three-dimensional (3D) DNA skeleton of the captured Ag-MBdsDNA via π-π stacking. Due to their good self-catalytic activity of labeled AgNPs, more silver was deposited on the Ag-MBdsDNA@GQDs, giving rise to further amplification of expected signal. With four types of cancer cells as models, MCF-7, CCRF-CEM, HeLa, and K562 cells were assayed in the ranges of 1.0 × 102-1.0 × 107, 1.5 × 102-2.0 × 107, 2.0 × 102-5.0 × 106, and 1.2 × 102-2.0 × 106 cells mL-1 with the detection limits of 38, 53, 67, and 42 cells mL-1, respectively. Notably, this strategy supplies a simple and versatile platform for sensitive determination of multiple targeted cells, which would play a crucial role in point-of-care diagnostic fields.

Internal Light Source-Driven Photoelectrochemical 3D-rGO/Cellulose Device Based on Cascade DNA Amplification Strategy Integrating Target Analog Chain and DNA Mimic Enzyme

In this work, a chemiluminescence-driven collapsible greeting card-like photoelectrochemical lab-on-paper device (GPECD) with hollow channel was demonstrated, in which target-triggering cascade DNA amplification strategy was ingeniously introduced. The GPECD had the functions of reagents storage and signal collection, and the change of configuration could control fluidic path, reaction time and alterations in electrical connectivity. In addition, three-dimentional reduced graphene oxide affixed Au flower was in situ grown on paper cellulose fiber for achieving excellent conductivity and biocompatibility. The cascade DNA amplification strategy referred to the cyclic formation of target analog chain and its trigger action to hybridization chain reaction (HCR), leading to the formation of numerous hemin/G-quadruplex DNA mimic enzyme with the presence of hemin. Subjected to the catalysis of hemin/G-quadruplex, the strong chemiluminiscence of luminol-H2O2 system was obtained, which then was used as internal light source to excite photoactive materials realizing the simplification of instrument. In this analyzing process, thrombin served as proof-of-concept, and the concentration of target was converted into the DNA signal output by the specific recognition of aptamer-protein and target analog chain recycling. The target analog chain was produced in quantity with the presence of target, which further triggered abundant HCR and introduced hemin/G-quadruplex into the system. The photocurrent signal was obtained after the nitrogen-doped carbon dots sensitized ZnO was stimulated by chemiluminescence. The proposed GPECD exhibited excellent specificity and sensitivity toward thrombin with a detection limit of 16.7 fM. This judiciously engineered GPECD paved a luciferous way for detecting other protein with trace amounts in bioanalysis and clinical biomedicine.

Double signal amplification based on palladium nanoclusters and nucleic acid cycles on a μPAD for dual-model detection of microRNAs

MicroRNAs (miRNAs) are a class of significant biomarkers; however, it is still a huge challenge to express them accurately. Herein, a fluorescent/colorimetric dual-model biosensor based upon the quenching effect of graphitic carbon nitride on palladium nanoclusters (Pd NCs) on the platform of a microfluidic paper-based analytical device was built for the detection of miRNAs. On the one hand, Pd NCs could catalyze a chromogenic reaction so that preliminary detection was achieved by the naked eye. On the other hand, the fluorescence analysis combined with nucleic acid cycle signal amplification was required to get precise result and the detection limit is 3 fM, which was superior to the previous method. Whats more, this biosensor could be designed to detect other miRNAs via changing the corresponding aptamer sequences. Therefore, the as-constructed biosensor supplies a versatile platform to conduct point-of-care detection of miRNAs with outstanding performance.