Trends in Analytical Chemistry (v.39, #C)

In the news (v-xii).

New materials in analytical chemistry by Gangfeng Ouyang (1-2).

► Intracellular small-molecule reactive species are important signaling molecules. ► Functional probes for imaging Intracellular small-molecule reactive species (ISMRS). ► We discuss classification and strategies of developing functional probes. ► We review nanoprobes for multi-functional detection and therapeutic application.We summarize recent progress in imaging intracellular small-molecule reactive species (ISMRS) by functional probes. In molecular imaging, functional fluorescent and luminescent probes (e.g., ratiometric, targetable fluorescent, reversible fluorescent, and multi-functional) and corresponding nanoprobes have great potential for investigating ISMRS-mediated cell-signal transduction. We describe design strategies for the development of functional probes. Future research on ISMRS will benefit from recent advances in the development of new functional probes for selective detection of ISMRS.
Keywords: Intracellular small-molecule reactive species (ISMRS); Fluorescent probe; Luminescent probe; Molecular imaging; Multi-functional probe; Nanoprobe; Ratiometric probe; Reversible probe; Targetable probe;

Nanomaterials in analytical atomic spectrometry by Xiaoming Jiang; Ke Huang; Dongyan Deng; Hui Xia; Xiandeng Hou; Chengbin Zheng (38-59).
► Nanomaterials used in analytical atomic spectrometry for preconcentration/separation. ► Nanomaterials are used in analytical atomic spectrometry to enhance sensitivity. ► Elemental impurities in nanomaterials determined by analytical atomic spectrometry. ► Nanomaterials can be characterized by using analytical atomic spectrometry.Nanomaterials have attracted considerable interest in analytical chemistry (e.g., sample pre-concentration, molecular probes, and biological and electrochemical sensing). However, their physico-chemical and surface properties are significantly affected by their size and morphology, and impurities.This article reviews the general applications of nanomaterials in analytical atomic spectrometry, including their use to improve the sensitivity and the selectivity of atomic spectrometric methods, to broaden the application range to biological-molecule detection, and to characterize and to determine nanomaterials themselves and their impurities.
Keywords: Atomic spectrometry; Biological-molecule detection; Chemical-vapor generation; Immunoassay; Nanomaterial; Nanomaterial impurity; Selectivity; Sensitivity; Solid-phase extraction; Speciation analysis;

Lanthanide ion-based luminescent nanomaterials for bioimaging by Chenzhong Yao; Chenzhong Yao; Yexiang Tong (60-71).
► We describe the advancements in lanthanide luminescent bio-probes. ► We highlight selection of host materials, emitting activator ions and sensitizers. ► Surface functionalization is useful to improve the hydrophilicity of nanoparticles. ► We review new trends in luminescent nanoparticles for bioimaging.Lanthanide ion-based luminescent nanomaterials have been developed for their unique properties (i.e. long lifetime, narrow full width at half maximum for emission peaks, and large Stokes shift). It is still a big challenge to construct new luminescent nanoparticles (NPs) with good biocompatibility for biological applications.In this review, we describe the advancements in up-conversion of lanthanide NPs and long-lasting luminescent NPs. We include mechanisms, selection, surface functionalization and applications in bioimaging.
Keywords: Biocompatibility; Bioimaging; Lanthanide; Luminescence; Nanomaterial; Nanoparticle; Near-infrared excitation; Photoluminescence; Surface functionalization; Up-conversion;

Aptamer-conjugated optical nanomaterials for bioanalysis by Quan Yuan; Danqing Lu; Xiaobing Zhang; Zhuo Chen; Weihong Tan (72-86).
► Research is urgent for aptamer-conjugated optical nanomaterials in bioanalysis. ► Quantum dots and carbon nanotubes are aptamer-conjugated fluorescent nanomaterials. ► Aptamer-functionalized plasmonic metal nanomaterials for SPR and SERS detection. ► Aptamer-conjugated nanomaterials as fluorescence quenchers for biodetection. ► Carbon nanotubes, graphene, gold nanoparticles and dye-doped silica nanoparticles.We review advances in the development and the application of optical biosensing systems based on aptamers. Aptamers exhibit advantages as molecular recognition elements for biosensors when compared to traditional antibodies. Among different detection modes that have been employed, optical methods are among the most used, and the combination of aptamers with novel optical nanomaterials has significantly improved the performance of aptamer-based sensors.The review briefly introduces the unique optical properties of nanoscale materials and the urgency of research on aptamer-conjugated optical nanomaterials in bioanalysis. We then discuss current research activities with typical examples of fluorescence, surface-plasmon resonance and quencher nanomaterials for different detection methods (e.g., fluorescence resonance transfer, colorimetry, and surface-enhanced Raman scattering spectroscopy). The conclusion summarizes this exciting realm of study and offers perspectives for future developments.
Keywords: Aptamer; Bioanalysis; Biosensor; Colorimetry; Fluorescence; Nanomaterial; Optical sensing; Quencher; Surface-enhanced Raman scattering spectroscopy; Surface-plasmon resonance;

Graphenes in chemical sensors and biosensors by Sven Kochmann; Thomas Hirsch; Otto S. Wolfbeis (87-113).
► We cover the current state of the art of using graphenes in sensor applications. ► We classify each type of graphene. ► We discuss unmodified materials and composite materials. ► This review is based on ∼270 references from 2007–12.This review covers the current state of the art of using graphenes in electrochemical and optical chemical sensors and biosensors. We first discuss the various types of graphenes, graphene oxides and the like, and also give a definition for each. This is followed by a section on the use of non-modified materials (“plain graphenes”) in mainly electrochemical and optical chemical sensors and biosensors. The next section summarizes the various kinds of sensors based on composite materials containing graphenes, with subsections on electro-chemical, field-effect-transistor-based, fluorescent, chemiluminescent and colorimetric sensors. We show that the use of graphenes alone or in composite form can improve the performance of chemical sensors and biosensors, particularly with respect to dynamic ranges, lower limits of detection, selectivity and size of instrumentation. The review is based on ∼270 references, primarily from 2007–12.
Keywords: Biosensor; Chemical sensor; Chemiluminescence; Electrochemical sensor; Field-effect transistor; Fluorescence; Graphene; Graphene oxide; Nanocomposite; Reduced graphene oxide (rGO);

Analytical and environmental applications of nanoparticles as enzyme mimetics by Jianxin Xie; Xiaodan Zhang; Hui Wang; Huzhi Zheng; Yuming Huang; Jianxin Xie (114-129).
► Analytical and environmental applications of nanoparticles (NPs) as enzyme mimetics. ► Review covers magnetic nanoparticles (NPs), cerium-oxide NPs and noble-metal NPs. ► Screening tools include colorimetric, electrochemical and chemiluminescence methods. ► Discussion of the future outlook of nanoparticles (NPs) as enzyme mimetics.Recently, the intrinsic enzyme-like activity of nanoparticles (NPs) has become a growing area of interest. Compared with natural enzymes, these enzyme-like NPs are stable against denaturing, low in cost, and highly resistant to high concentrations of substrate. These advantages make them promising in various applications.In this review, we focus on recent advances in NPs as enzyme mimetics and their analytical and environmental applications. We pay special attention to the enzyme-like activity of magnetic NPs, cerium-oxide NPs, noble-metal NPs, carbon and other nanomaterials.
Keywords: Biochemical analysis; Carbon nanomaterial; Cerium-oxide nanoparticle; Colorimetric biosensing; Degradation; Electrochemical biosensing; Enzyme mimetic; Iron-oxide magnetic nanoparticle; Noble-metal nanoparticle; Organic pollutant;

► Work on electrochemical (EC) biosensors for protein function analysis is reviewed. ► Focus is on label-free EC sensors based on electrocatalytic oxidation of tyrosines. ► Studies on protein conformation change and ligand binding are described. ► Detection of protein oxidative damage and protein phosphorylation is described.Label-free electrochemical (EC) protein biosensors that derive electrical signal from redox-active amino acid (AA) residues can avoid disruption of delicate protein structures, and thus provide a great opportunity to reveal valid information about protein functions. However, the challenge is that such a signal is usually very limited due to the sluggish EC reaction of free AAs on most common electrodes and slow electron-transfer rates from the deeply-buried AA residues in a protein to the electrode. Signal enhancement therefore becomes crucial. We first survey recent progress in this area.We present a signal-enhancing system that relies on the electrocatalytic oxidation of tyrosine mediated by osmium bipyridine or phenoxazine complexes. We describe several applications of label-free protein EC biosensors based on this detection principle for the analysis of protein functions, including the monitoring of protein-conformation change, study of ligand/protein binding, and detection of protein oxidative damage and protein phosphorylation.We describe related works on protein-function analysis using other signal-enhancing methods. The results suggest that label-free EC protein biosensors are suitable for the rapid survey of protein functions due to their fast response, ease of integration, cost effectiveness and convenience. Proof-of-concept work on the application of our system is paving the way for bio-analytical detections and protein-function analysis in future work.
Keywords: Bioanalytical detection; Biosensor; Electrocatalytic oxidation; Electrochemistry; Label-free protein biosensor; Osmium bipyridine; Phenoxazine; Signal enhancement; Protein function; Tyrosine;

Bioanalysis based on nanoporous materials by Zhihui Dai; Huangxian Ju (149-162).
► Nanoporous materials possess many advantages in their bioanalytical applications. ► Nanoporous materials significantly improve the analytical performance of biosensors. ► Recent advances in bioanalytical applications of nanoporous materials are highlighted.Nanoporous materials possess nanometer-sized pore distribution and are widely used in biosensing. The unique properties of nanoporous materials include large surface area, good chemical, thermal and mechanical stability, very uniform pore distribution with tunable pore size, high adsorption capacity, and an ordered porous network for free diffusion of substrates and reaction products.Usage of nanoporous materials can significantly improve the analytical performance of biosensors in biomedical diagnosis and monitoring of food and environmental quality.This article reviews some major advances in bioanalysis based on nanoporous materials, including biosensing based on zeolite, mesoporous silica, mesoporous carbon, mesoporous metal and metal oxide. These nanoporous materials have shown promising applications in electrochemical biosensing, electrocatalysis, proteomics analysis and biorecognition.
Keywords: Bioanalysis; Biorecognition; Biosensing; Electrocatalysis; Electrochemical biosensor; Mesoporous material; Nanoporous material; Pore; Proteomics analysis; Zeolite;

Conducting polymers in environmental analysis by Xiang Li; Yonghua Wang; Xin Yang; Jianmin Chen; Hongbo Fu; Tiantao Cheng; Yonghua Wang (163-179).
► This review deals with conducting polymers in analytical applications. ► Focus on sensors, separations and extraction techniques. ► The most important techniques for fabricating conducting polymers to aid analysis. ► Current use shows conducting polymers have great potential for future applications.As a family of materials, conducting polymers (CPs) elicit the possibility of both exploiting the chemical and physical attributes of the polymer for chemical analysis and incorporating its electronic and electrochemical properties to enhance the analytical figures of merit. This review article provides a snapshot of current investigations in many research laboratories on the use of CPs for sensors, separations and extraction techniques.This review focuses primarily on polyaniline, polypyrrole, and polythiophene and their substituted composites. It includes applications in gas, ion and organic molecule sensors, and solid-phase extraction and microextraction. We also discuss the broad challenges and the accomplishments in preparing analytical devices from CPs.
Keywords: Analytical device; Biosensor; Chemical analysis; Conducting polymer; Environmental analysis; Extraction; Sensor; Separation; Solid-phase extraction (SPE); Solid-phase microextraction (SPME);

Development of chiral stationary phases for high-performance liquid chromatographic separation by Mengling Tang; Jing Zhang; Shulin Zhuang; Weiping Liu (180-194).
► New types of chiral stationary phases (CSPs) are summed up and classified. ► Monolithic column CSPs offer advantages of low backpressure, efficiency and speed. ► Asymmetric organocatalysts are proposed as new kinds of chiral stationary phase (CSP). ► Novel design method for chiral stationary phases (CSPs) uses computational chemistry.Chromatography technology based on chiral stationary phases (CSPs) for enantioseparation is widely used for resolution and preparation of biochemicals (e.g., drugs, foods, fragrances and pollutants).In this review, we focus on the development of CSPs for high-performance liquid chromatography (HPLC), including the recognition mechanism, applications and limitations of classical CSPs, newly discovered types of CSP, and also the methods for the rational design of future CSPs on the basis of computational chemistry.
Keywords: Biochemical; Chiral stationary phase (CSP); Chromatography; Computational chemistry; Enantioseparation; High-performance liquid chromatography (HPLC); Preparation; Recognition; Rational design; Resolution;

Applications of nanomaterials in enantioseparation and related techniques by Cuilan Chang; Xin Wang; Yu Bai; Huwei Liu (195-206).
► Applications of nanomaterials in enantioselective technologies are summarized. ► Nanomaterials could improve the selectivity of enantioselective technologies. ► Nanomaterials could improve the stability of enantioselective technologies. ► Nanomaterials could improve the efficiency of enantioselective technologies. ► Magnetic materials help speed, simplicity and cost-effectiveness of enantioselection.Chirality is an important, universal phenomenon in nature. For the in-depth study of pharmacology and biology, efficient enantioselective technologies are indispensable. Nanomaterials with large surface-to-volume ratio and specific physical and chemical properties have demonstrated great potential in chiral discrimination. Many publications show that utilization of nanomaterials could improve the selectivity, the stability and the efficiency of enantioseparation.This review summarizes the applications of various enantioselective nanomaterials, including mesoporous silica, organic polymers, metal-organic frameworks, metal nanomaterials, magnetic nanomaterials, carbon nanotubes and well-oriented chiral nanolayers. After proper preparation and modification, these functionalized nanomaterials are effective for chiral separation through their specific enantioselective adsorption, especially when they are used as stationary or pseudo-stationary phases in chiral chromatographic separation, such as thin-layer chromatography, high-performance liquid chromatography, gas chromatography and capillary electrophoresis.
Keywords: Carbon nanotube; Enantioseparation; Magnetic nanomaterial; Mesoporous silica; Metal nanomaterial; Metal-organic framework; Nanomaterial; Organic polymer; Stationary phase;

Molecularly-imprinted monoliths for sample treatment and separation by Jin Tan; Zi-Tao Jiang; Rong Li; Xiu-Ping Yan (207-217).
► Molecularly-imprinted monoliths (MIMs) for sample preparation. ► Preparation and characterization of molecularly-imprinted monoliths (MIMs). ► Evaluation of the analytical performance of molecularly-imprinted monoliths (MIMs).Molecularly-imprinted monoliths (MIMs) are highly selective materials, which have shown great potential in sample pretreatment and chromatographic separation.In this review, we focus on recent progress in the application of MIMs in sample treatment and separation. We describe the preparation and the characterization of MIMs and discuss the evaluation of their analytical performance. We highlight the latest applications of MIMs to sample treatment, especially solid-phase extraction.
Keywords: Analytical performance; Chromatographic separation; Molecular imprinting; Molecularly-imprinted monolith (MIM); Monolith; Sample pretreatment; Sample treatment; Separation; Solid-phase extraction (SPE); Solid-phase microextraction (SPME);

Advances in analytical chemistry using the unique properties of ionic liquids by Zhi-qiang Tan; Jing-fu Liu; Long Pang (218-227).
► Unique properties make ionic liquids (ILs) attractive for analytical applications. ► Analytical chemistry has benefited from the unique properties of ionic liquids (ILs). ► Challenges and perspectives of applying ionic liquids (ILs) in analytical chemistry.Ionic liquids (ILs) are regarded as non-molecular solvents, as they are composed entirely of cations and anions. ILs possess several excellent unique properties (e.g., low volatility, high thermal stability, specific electrochemical characteristics, easy design, tunable viscosity, and miscibility with water or organic solvents). These properties make ILs attractive candidates for various analytical applications, the number of publications on which has increased exponentially in the past decade.This article presents an overview of representative applications of ILs in advances in analytical chemistry that benefited from the unique properties of ILs, including the development achieved by using ILs as extraction solvents, dissolution solvents and separation media.
Keywords: Chromatographic separation; Dissolution; Electrochemical characteristics; Extraction; Ionic liquid (IL); Microextraction; Miscibility; Separation; Task-specific extraction; Tunable viscosity;

► Materials-based approaches are essential in analytical sample preparation. ► We review recent developments of emerging materials in sample preparation. ► We focus on the merits and the shortcomings of materials in sample preparation.The marriage of materials and analytical chemistry has been an important development in sample preparation. Also, miniaturized sample preparation is gaining more interest, with the advantages of much lower consumption of organic solvents, improved labor efficiency and shorter extraction times.This review describes recent developments of sorbent-based sample-preparation methods, including primarily procedures for minimizing solvent usage and focusing on preparation and applications of interesting materials as sorbents.We discuss and assess several novel materials (i.e. graphene, ionic liquids, polymeric ionic liquids, molecularly-imprinted polymers, and metal-organic frameworks) in some of the latest published works on sample preparation.We emphasize the performance of these new sorbents in the extraction of analytes from environmental, biological and food samples, and evaluate their merits and shortcomings.
Keywords: Graphene; Ionic liquid (IL); Metal-organic framework (MOF); Molecularly-imprinted polymer (MIP); Polymeric ionic liquid (PIL); Sample preparation; Solid-phase extraction (SPE); Solid-phase microextraction (SPME); Solvent; Sorbent; See Appendix A before the Reference section at the end of the article.;

► Thin-film microextraction offers a new geometry for solid-phase microextraction. ► Experimental results show thin-film microextraction has good agreement with theory. ► To develop thin-film microextraction calibration is important for real applications. ► A desorption method is a challenge for thin film microextraction to be widely used. ► Review of application of thin-film microextraction to gas, liquid, solid sampling.As a new geometry for solid-phase microextraction, thin-film microextraction (TFME) has become an attractive sample-preparation technique. The high surface area-to-volume ratio together with the increase of extraction-phase volume enhanced the sensitivity of this technique without sacrificing the sampling time compared to other microextraction approaches. Comprehensive research has demonstrated the good agreement of the experimental data with the fundamental principle of this technique.In this review, we summarize the theory of the sampling process, the reported calibration methods and diverse TFME formats, different structures of the extraction phase and related preparation methods. Furthermore, we discuss approaches to TFME desorption, coupling with different analytical instruments and the main applications of this technique.
Keywords: Calibration; Desorption; Extraction phase; Microextraction; Sample preparation; Sampling; Solid-phase microextraction (SPME); Thin-film desorption; Thin-film microextraction (TFME); Thin-film preparation;

Microplasmas for analytical applications of lab-on-a-chip by Daibing Luo; Yixiang Duan (254-266).
► Microplasma as sample-excitation source for optical emission spectrometry. ► Development of microfabrication techniques for lab-on-a-chip devices. ► Miniaturized analytical instrumentation for chemical detection.The concept of “lab-on-a-chip” has expanded within recent years and has numerous potential applications in analytical chemistry. As a result, greater emphasis has been placed on research into microplasmas, which can act as sample-excitation sources for lab-on-a-chip devices. These miniaturized versions of full-sized plasma sources have become popular for optical emission spectrometry, mass spectrometry and atomic spectroscopy.Microplasmas for lab-on-a-chip can offer an element-specific or molecule-specific, label-free detection method. The development of microfabrication techniques makes it possible to integrate microplasma sources on chips within analytical instruments, reducing the operating and purchasing costs while increasing instrument portability.We review current and prospective generation, fabrication and application of microplasma chips in lab-on-a-chip research.
Keywords: Analytical application; Atomic spectroscopy; Element-specific detection; Label-free detection; Lab-on-a-chip; Mass spectrometry; Microplasma; Molecule-specific detection; Optical emission spectrometry;