Carbon nanomaterials are among the most broadly discussed, researched and applied of synthetic nanomaterials. The structural diversity of these materials provides an array of unique electronic, magnetic and optical properties, which when combined with their robust chemistry and ease of manipulation, makes them attractive candidates for sensor applications. Furthermore, the biocompatibility exhibited by many carbon nanomaterials has seen them used as in vivo biosensors. Carbon nanotubes, graphene and carbon dots have come under intense scrutiny, as either discrete molecular-like sensors, or as components which can be integrated into devices. In this review we consider recent developments in the use of carbon nanoparticles and nanostructures as sensors and consider how they can be used to detect a diverse range of analytes.

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Recent developments in carbon nanomaterial sensors

The widespread exploitation of biosensors in the analysis of molecular recognition has its origins in the mid-1990s following the release of commercial systems based on surface plasmon resonance (SPR). More recently, platforms based on piezoelectric acoustic sensors (principally 'bulk acoustic wave' (BAW), 'thickness shear mode' (TSM) sensors or 'quartz crystal microbalances' (QCM)), have been released that are driving the publication of a large number of papers analysing binding specificities, affinities, kinetics and conformational changes associated with a molecular recognition event. This article highlights salient theoretical and practical aspects of the technologies that underpin acoustic analysis, then reviews exemplary papers in key application areas involving small molecular weight ligands, carbohydrates, proteins, nucleic acids, viruses, bacteria, cells and lipidic and polymeric interfaces. Key differentiators between optical and acoustic sensing modalities are also reviewed.

A survey of the 2001 to 2005 quartz crystal microbalance biosensor literature: applications of acoustic physics to the analysis of biomolecular interactions.

Surface acoustic wave sensors in the bioanalytical field: Recent trends and challenges

A PVC membrane sensor for mercury(II) ions based on hexathia-18-crown-6-tetraone as membrane carrier was prepared. The sensor exhibits a Nernstian response for Hg2+ ions over a wide concentration range (1.0 × 10-3−4.0 × 10-6 M). It has a relatively fast response time and can be used for at least 3 months without any considerable divergence in potentials. The proposed sensor revealed very good selectivities for Hg2+ over a wide variety of other metal ions and could be used in a pH range of 0.5−2.0. It was used as an indicator electrode in potentiometric titration of mercury ions.

PVC-Based Hexathia-18-crown-6-tetraone Sensor for Mercury(II) Ions

Functionalized fullerene (C60) as a potential nanomediator in the fabrication of highly sensitive biosensors

Artificial macrocyclic polyethers were synthesized and applied as ion-selective electrode neutral carriers in PVC electrode membranes, ion-chromatographic packing materials, extractants and adsorbents for ion separations, phase-transfer catalysts for organic reactions, surfactants, liquid crystals and ion-transport carriers through liquid membranes. Ion selective electrodes such as K+, Na+, UO22+, Cs+, Pb2+ and Fe3+, Hg2+ and Ag+ ion electrodes based on crown ether - phosphotungstic acid (PW) precipitates and dithio crown ethers respectively were prepared and showed good sensitivity and selectivity. Crown ether - PW precipitates were also applied as adsorbents for adsorptions of rare-earth ions and some common heavy metal ions. Some rare-earth ions were found to be easily extracted with crown ethers especially 15-crown-5. Poly(styrene/divinyl benzene)-cryptand 22 resin was synthesized and applied as a bifunctional stationary phase of ion chromatography for separations of both cations and anions even some organic carboxylate geometric isomers A so called “drift-type” crown ether catalyst and some common crown ether catalysts were applied to catalyze organic oxidation, reduction, substitution and anionic polymerization. The effect of salts on micellar formation and stability, of liquid crystals of some crown-ether surfactants were investigated. Some special crown-ether carriers were also prepared and applied for Na+, K+ and Mg2+ ion transport through liquid membranes.

Application of Macrocylic Polyethers

A reusable and sensitive piezoelectric quartz crystal detector was developed for the detection of either cations or anions in ion chromatography. The quartz crystal electrode coated with crown ether (sym-dibenzo-16-crown-5-oxydodecanic acid) was prepared and was found to give the best results in terms of stability, sensitivity and reproducibility. Linear frequency (voltage) responses on a 10 MHz AT-cut crystal for ions were found on the range 0.1–5 × 10–5 mol l–1. Variations of the crystal frequencies were converted to voltage using a TC 9400 chip. Polystyrene–poly(divinyl benzene) with cryptand [2,2] as an anchoring group was synthesized and applied as a bifunctional ion chromatographic packing material for the separation of both cations and anions. The crown ether coated piezoelectric crystal detector with detection limits of 2 × 10–5(1 × 10–10 mol)–5 × 10–5 mol l–1(2.5 × 10–10 mol) for various ions showed a similar detection limit to that of a commercial conductivity detector in ion chromatography. The effects of solvents, reproducibility of responses and competitiveness with respect to a commercial conductivity detector were also investigated.

Application of crown ether coated piezoelectric crystal as a detector for ion chromatography

A mixed-valence cluster of cobalt(II) hexacyanoferrate and fullerene C60-enzyme-based electrochemical glucose sensor was developed. A water insoluble fullerene C60-glucose oxidase (C60-GOD) was prepared and applied as an immobilized enzyme on a glassy carbon electrode with cobalt(II) hexacyanoferrate for analysis of glucose. The glucose in 0.1 M KCl/phosphate buffer solution at pH = 6 was measured with an applied electrode potential at 0.0 mV (vs Ag/AgCl reference electrode). The C60-GOD-based electrochemical glucose sensor exhibited efficient electro-catalytic activity toward the liberated hydrogen peroxide and allowed cathodic detection of glucose. The C60-GOD electrochemical glucose sensor also showed quite good selectivity to glucose with no interference from easily oxidizable biospecies, e.g. uric acid, ascorbic acid, cysteine, tyrosine, acetaminophen and galactose. The current of H2O2 reduced by cobalt(II) hexacyanoferrate was found to be proportional to the concentration of glucose in aqueous solutions. The immobilized C60-GOD enzyme-based glucose sensor exhibited a good linear response up to 8 mM glucose with a sensitivity of 5.60 × 102 nA/mM and a quite short response time of 5 sec. The C60-GOD-based glucose sensor also showed a good sensitivity with a detection limit of 1.6 × 10-6 M and a high reproducibility with a relative standard deviation (RSD) of 4.26%. Effects of pH and temperature on the responses of the immobilized C60-GOD/cobalt(II) hexacyanoferrate-based electrochemical glucose sensor were also studied and discussed.

Immobilized Fullerene C60‐Enzyme‐Based Electrochemical Glucose Sensor

A drift-type phase transfer catalyst, cryptand-22, adsorbed on poly(styrene/diviny benzene)-sulfonic resin was prepared and applied to catalyze the reduction of ketones, e.g., acetophenone, benzophenone and benzaldehyde with NaBH4 as a reducing agent. Before the reaction, cryptand-22 was adsorbed on the sulfonic resin with ion-pairing, resin-SO3− +NH-cryptand-22. The ion-pairs can be destroyed by adjusting the basicity of the reaction solution with NaOH and the cryptand can be released from the resin into the reaction solution as a homogeneous catalyst during the reaction period. After the reaction, the cryptand catalyst can be readsorbed on the resin by adjusting the acidity of the solution with HCl and can be readily recovered by filtration like a heterogeneous catalyst. The draft-type cryptand catalyst exhibited better catalytic ability than some common crown ethers, e.g., 15-crown-5, benzo-15-crown-5, 12-crown-4 and dibenzo-18-crown-6 for the reduction of acetophenone with NaBH4. Effects of solvents, pH of solutions, concentration of the catalyst, reducing agents and resin property on the reduction of ketones were investigated and discussed. The reaction mechanism of the cryptand catalyzed reduction was also studied.

Application of Cryptand/Polystyrene Drift-Type Phase Transfer Catalysts for Reduction of Ketones

Poly (styrene/divinyl benzene) with cryptand 22 as an anchoring group was synthesized and applied as a bifunctional packing material for the separation of both cations and anions. At pH 10, the resin became a cation exchanger and successfully separated alkali metal ions such as Li+, K+ and Cs+ with methanol as eluent. The effects of solvents, flow rate and temperature on the separation of various ions were also investigated.

Jeng-Shong Shih

Papers

Application of Macrocylic Polyethers

Application of crown ether coated piezoelectric crystal as a detector for ion chromatography

Immobilized Fullerene C60‐Enzyme‐Based Electrochemical Glucose Sensor

Application of Cryptand/Polystyrene Drift-Type Phase Transfer Catalysts for Reduction of Ketones

The Application of Cryptand 22 as a Bifunctional Stationary Phase for Ion Chromatography