Functionalized nanocomposites based on various type of graphene nanomaterials including graphene, graphene oxides (GOs), and doped graphene (oxides) are widely used as materials for various sensors that can display high sensitivity, selectivity and stability. This review with 347 references summarizes advances in the preparation and functionalization of graphene nanocomposites for the application of electrochemical sensors and biosensors. Following a general introduction into the field, the article is divided into subsections on (a) the synthesis and functionalization of nanocomposites (made from graphene, various kinds of GOs, heteroatom-doped GOs), (b) on methods for functionalization of composites (with other carbon nanomaterials, metal nanoparticles, metal oxide and metal sulfide nanoparticles), (c) on functionalization with inorganic materials including polyoxometalates, hexacyanoferrates, minerals), (d) on functionalization with organic materials such as amino acids, surfactants, organic dyes, ionic liquids, macrocycles (including cyclodextrins, crown ethers and calixarenes), and (e) on functionalization with organometallics and with various other organic compounds, (f) on functionalizations with polymers such as conventional polymers, polyelectrolytes, conducting polymers, molecularly imprinted polymers, (g) on functionalization with biomolecules including proteins and nucleic acids. Other subsections cover flexible graphene and GO based nanocomposites and 3D composites. Application of graphene and GO nanocomposites are then covered in a in large section that comprises electrochemical sensors and biosensors (based on voltammetry, amperometry, potentiometry, impedimetry, electrochemiluminescence, photoelectrochemistry, field effect transistors, electrochemical immunosensors) with specific subsections on gas sensors, enzymatic biosensors and gene sensors. A concluding section covers current challenges and perspectives of graphene and GO based (bio)sensing.

Nanocomposites of graphene and graphene oxides: Synthesis, molecular functionalization and application in electrochemical sensors and biosensors. A review

Due to their unique and fascinating properties, polymer nanocomposites (PNCs) have been extensively studied in recent years. PNCs can be synthesized in several different nanoscale forms with minimal effort, thus allowing the fabrication of various novel chemical and biological sensors. This review covers recent applications based on PNCs for the fabrication of electrochemical sensors, biosensors, including DNA biosensors, immunosensors, and aptamer sensors. To improve the sensor performance, nanocomposites have been reported in various combinations such as conductive polymers with graphene (Grp), carbon nanotubes (CNTs), and metal nanoparticles, which endow high electrical conductivity, effective surface area, and fast electron transfer rate.

Next-generation polymer nanocomposite-based electrochemical sensors and biosensors: A review

The interactions between polyphenols, especially flavonoids and plasma proteins, have attracted great interest among researchers. Few papers, however, have focused on the structure-affinity relationship of polyphenols on their affinities for plasma proteins. The aim of this review is to give an overview of the research reports on the characterization, influence on the bioactivity, and the structure-affinity relationship for studying the affinities between polyphenols and plasma proteins. The molecular properties that influence the affinities of polyphenols for plasma proteins are the following: 1) One or more hydroxyl groups in the B-ring (e.g., 3',4' dihydroxylated B ring catechol group) of flavonoids enhanced the binding affinities to proteins. However, the hydroxyl group in the C-ring will weaken the binding interaction. 2) The presence of an unsaturated 2,3-bond in conjugation with a 4-carbonyl group, characteristic of flavonols structure, has been associated with stronger binding affinity with plasma proteins; 3) The glycosylation of flavonoids decreases the affinities for plasma proteins by 1-3 orders of magnitude depending on the conjugation site and the class of sugar moiety; 4) The methylation of hydroxyl groups in flavonoids slightly enhanced the affinities for plasma proteins by 2-16 times; 5) The galloylated catechins have higher binding affinities for plasma proteins than do non-galloylated catechins and the pyrogallol-type catechins have higher affinities than do the catechol-type catechins. The affinity of the catechin with 2,3-trans structure was lower than those of the catechin with 2,3-cis structure; 6) The gallotannins with more gallol groups presented a much higher percentage of binding to plasma proteins. α-D-Gallotannin showed a greater affinity for plasma proteins than does the natural stereoisomer, β-D-gallotannin; 7) The binding degree of chlorogenic acid with only one caffeoyl group was lower than the binding degrees of caffeoyl quinic acids with more caffeoyl groups. The methylation of phenolic acid decreased the affinity for BSA.

A review of dietary polyphenol-plasma protein interactions: characterization, influence on the bioactivity, and structure-affinity relationship.

Fabrication of transition metal selenides and their applications in energy storage

In this work, the interaction of a naturally occurring chromene, flindersine (FL), and bovine serum albumin (BSA) has been investigated by UV-vis absorption and fluorescence spectroscopy, time-resolved lifetime measurements, steady state photochemistry, and semiempirical calculations. The interplay of FL with tryptophan (Trp) has been studied in parallel. The interaction of FL with BSA causes fluorescence quenching of BSA through both static and dynamic quenching mechanisms. FL binds BSA with a stoichiometry that varies from 1.09:1 to 0.80:1 as the temperature increases from 293 to 308 K. The reaction is characterized by negative enthalpy (deltaH degrees = -193 kJ mol(-1)) and negative entropy (deltaS degrees = -550 J K(-1) mol(-1)), indicating that the predominant forces in the FL-BSA complex are hydrogen bonding and van der Waals forces. The binding distance between the protein and the photochrome was calculated as 2.5 nm, according to the Foerster theory on resonance energy transfer. The effect of FL concentration on the BSA fluorescence was analyzed according to the maximum entropy method. FL also quenches the emission of Trp with a mechanism that, based on the experimental evidence, excludes both static and dynamic effects. An alternative relaxation pathway, consisting in an electron transfer from a prefluorescent state of Trp to FL, is put forward. The photobehavior of FL is affected by the interplay with BSA but not with Trp. When FL is complexed with BSA, it becomes a more fluorescent and more reactive species. Semiempirical calculations of the lowest optically active electronic transitions of hypothetical FL photoproducts suggest the most likely structure for the photoproduct.

Static and dynamic interaction of a naturally occurring photochromic molecule with bovine serum albumin studied by UV-visible absorption and fluorescence spectroscopy.

High-selective and sensitive voltammetric sensor for butylated hydroxyanisole based on AuNPs–PVP–graphene nanocomposites

Sensitive voltammetric sensor based on isopropanol-Nafion-PSS-GR nanocomposite modified glassy carbon electrode for determination of clenbuterol in pork.

In this work, a very sensitive electrochemical sensor for Sudan I was established based on nanohybrids of graphene-ZnSe quantum dots. Positively charged cetyltrimethyl-ammonium bromide (CTAB) functionalized graphene was used as a template-directed building block to self-assemble negatively charged ZnSe quantum dots (QDs). The hybrids of ZnSe-CTAB-graphene exhibited strong enrichment effect on Sudan I and gave superior electrocatalytic activity towards the oxidation of Sudan I. Applying differential pulse voltammetry (DPV), the peak current of Sudan I is proportional to its concentration in the range from 0.004 to 2.0 μM and 2.0 to 15.0 μM. This report is the first on applying graphene-ZnSe hybrids for electrochemical sensing.

High-sensitive electrochemical sensor of Sudan I based on template-directed self-assembly of graphene-ZnSe quantum dots hybrid structure

Electrostatic repulsion strategy for high-sensitive and selective determination of dopamine in the presence of uric acid and ascorbic acid.

A highly selective and sensitive electrochemical sensor for tryptophan based on the excellent surface adsorption and electrochemical properties of PSS functionalized graphene.

Ling Wang

Papers

High-selective and sensitive voltammetric sensor for butylated hydroxyanisole based on AuNPs–PVP–graphene nanocomposites

Sensitive voltammetric sensor based on isopropanol-Nafion-PSS-GR nanocomposite modified glassy carbon electrode for determination of clenbuterol in pork.

High-sensitive electrochemical sensor of Sudan I based on template-directed self-assembly of graphene-ZnSe quantum dots hybrid structure

Electrostatic repulsion strategy for high-sensitive and selective determination of dopamine in the presence of uric acid and ascorbic acid.

A highly selective and sensitive electrochemical sensor for tryptophan based on the excellent surface adsorption and electrochemical properties of PSS functionalized graphene.