Detection of chemical and biological agents plays a fundamental role in biomedical, forensic and environmental sciences1–4 as well as in anti bioterrorism applications.5–7 The development of highly sensitive, cost effective, miniature sensors is therefore in high demand which requires advanced technology coupled with fundamental knowledge in chemistry, biology and material sciences.8–13

In general, sensors feature two functional components: a recognition element to provide selective/specific binding with the target analytes and a transducer component for signaling the binding event. An efficient sensor relies heavily on these two essential components for the recognition process in terms of response time, signal to noise (S/N) ratio, selectivity and limits of detection (LOD).14,15 Therefore, designing sensors with higher efficacy depends on the development of novel materials to improve both the recognition and transduction processes. Nanomaterials feature unique physicochemical properties that can be of great utility in creating new recognition and transduction processes for chemical and biological sensors15–27 as well as improving the S/N ratio by miniaturization of the sensor elements.28

Gold nanoparticles (AuNPs) possess distinct physical and chemical attributes that make them excellent scaffolds for the fabrication of novel chemical and biological sensors (Figure 1).29–36 First, AuNPs can be synthesized in a straightforward manner and can be made highly stable. Second, they possess unique optoelectronic properties. Third, they provide high surface-to-volume ratio with excellent biocompatibility using appropriate ligands.30 Fourth, these properties of AuNPs can be readily tuned varying their size, shape and the surrounding chemical environment. For example, the binding event between recognition element and the analyte can alter physicochemical properties of transducer AuNPs, such as plasmon resonance absorption, conductivity, redox behavior, etc. that in turn can generate a detectable response signal. Finally, AuNPs offer a suitable platform for multi-functionalization with a wide range of organic or biological ligands for the selective binding and detection of small molecules and biological targets.30–32,36 Each of these attributes of AuNPs has allowed researchers to develop novel sensing strategies with improved sensitivity, stability and selectivity. In the last decade of research, the advent of AuNP as a sensory element provided us a broad spectrum of innovative approaches for the detection of metal ions, small molecules, proteins, nucleic acids, malignant cells, etc. in a rapid and efficient manner.37



Figure 1

Physical properties of AuNPs and schematic illustration of an AuNP-based detection system.



In this current review, we have highlighted the several synthetic routes and properties of AuNPs that make them excellent probes for different sensing strategies. Furthermore, we will discuss various sensing strategies and major advances in the last two decades of research utilizing AuNPs in the detection of variety of target analytes including metal ions, organic molecules, proteins, nucleic acids, and microorganisms.

/pdf/gold-nanoparticles-in-chemical-and-biological-sensing-5e2qojkdzn.pdf

Gold nanoparticles in chemical and biological sensing.

http://pubs.acs.org/doi/pdf/10.1021/cr400546e

Fluorescent Sensors for Measuring Metal Ions in Living Systems

Isothermal amplification of nucleic acids is a simple process that rapidly and efficiently accumulates nucleic acid sequences at constant temperature. Since the early 1990s, various isothermal amplification techniques have been developed as alternatives to polymerase chain reaction (PCR). These isothermal amplification methods have been used for biosensing targets such as DNA, RNA, cells, proteins, small molecules, and ions. The applications of these techniques for in situ or intracellular bioimaging and sequencing have been amply demonstrated. Amplicons produced by isothermal amplification methods have also been utilized to construct versatile nucleic acid nanomaterials for promising applications in biomedicine, bioimaging, and biosensing. The integration of isothermal amplification into microsystems or portable devices improves nucleic acid-based on-site assays and confers high sensitivity. Single-cell and single-molecule analyses have also been implemented based on integrated microfluidic systems. In this review, we provide a comprehensive overview of the isothermal amplification of nucleic acids encompassing work published in the past two decades. First, different isothermal amplification techniques are classified into three types based on reaction kinetics. Then, we summarize the applications of isothermal amplification in bioanalysis, diagnostics, nanotechnology, materials science, and device integration. Finally, several challenges and perspectives in the field are discussed.

Isothermal Amplification of Nucleic Acids

Gold nanorods have received much attention due to their unique optical and electronic properties which are dependent on their shape, size, and aspect ratio. This article covers in detail the synthesis, functionalization, self-assembly, and sensing applications of gold nanorods. The synthesis of three major types of rods is discussed: single-crystalline and pentahedrally-twinned rods, which are synthesized by wet chemistry methods, and polycrystalline rods, which are synthesized by templated deposition. Functionalization of these rods is usually necessary for their applications, but can often be problematic due to their surfactant coating. Thus, general strategies are provided for the covalent and noncovalent functionalization of gold nanorods. The review will then examine the significant progress that has been made in controllable assembly of nanorods into various arrangements. This assembly can have a large effect on measurable properties of rods, making it particularly applicable towards sensing of a variety of analytes. Other types of sensing not dependent on nanorod assembly, such as refractive-index based sensing, are also discussed.

Functional Gold Nanorods: Synthesis, Self-Assembly, and Sensing Applications

With over 2,000 publications, including about 250 reviews, resulting from a SciFinder search in just a two year period (2009–2010), the field of aptamer research has continuously generated lots of interest in the scientific community. Aptamers, first reported by three groups independently in 1990,1–3 are the artificial single-stranded DNA or RNA sequences (more recently, peptides) that fold into secondary and tertiary structures making them bind to certain targets with extremely high specificity. Owing to the high specific affinity of an aptamer to its target molecule (small molecules, proteins and even entire cells), it is thought to resemble chemical antibodies, with the dissociation constants ranging from nanomolar to picomolar level. Aptamers have a number of unique features which make them a more effective choice than antibodies. First, aptamers can be screened via in vitro process against a synthetic library, making it possible to target any molecules (from small inorganic ions to intact cells), overcoming the limit of having to use cell lines or animals, as is necessary for antibodies. Second, aptamers, once selected, can undergo subsequent amplification through polymerase chain reaction to produce a large quantity with high purity. Third, the simple chemical structure of aptamer makes it easily amendable to further modifications with functional groups according to different purposes. Finally, aptamers are much more stable than antibodies, making them suitable in applications requiring harsh conditions (e.g., high temperature or extreme pH).

The applications of aptamers remain very dynamic, with increasing explorations in the fields of biosensing, diagnostics and therapeutics (some aptamer-based applications are illustrated in Figure 1). There have been a numbers of excellent reviews in recent years with different emphases.4–8 Herein, as the first review of aptamers on Analytical Chemistry, we attempt to cover major progresses in bioanalytical applications of aptamers in the past 2 years.



Figure 1

The widespread use of aptamers for numerous analytical and biological applications. Bioanalytical applications of aptamers are highlighted in red.

Aptamer in bioanalytical applications.

The upregulation of microRNA (miRNA) is highly related with some kinds of tumor, such as breast, prostate, lung, and pancreatic cancers. Therefore, for an important tumor biomarker, the point-of-care testing (POCT) of miRNA is of significant importance and is in great demand for disease diagnosis and clinical prognoses. Herein, a POCT assay for miRNA detection was developed via a portable pressure meter. Two hairpin DNA probes, H1 and H2, were ingeniously designed and functionalized with magnetic beads (MBs) and platinum nanoparticles (PtNPs), respectively, to form MBs-H1 and PtNPs-H2 complexes. In the presence of target microRNA 21 (miR-21), the cyclic strand displacement reaction (SDR) between MBs-H1 and PtNPs-H2 was triggered to continuously form the MBs-H1/PtNPs-H2 duplex. Owing to the amplification of cyclic SDR, numerous PtNPs were enriched onto the surface of MBs to catalytically decompose H2O2 for the generation of much O2. The gas pressure value has a linear relationship with the logarithmic valu...

Ultrasensitive and Facile Detection of MicroRNA via a Portable Pressure Meter.

Discovering efficient antibacterial materials is crucial in the area of increasing drug resistance. Herein, we synthesized carbon dots (C-dots) with superior antibacterial activity through a simple...

One-Step and One-Precursor Hydrothermal Synthesis of Carbon Dots with Superior Antibacterial Activity

Plant tissue-based chemiluminescence flow biosensor for determination of unbound dopamine in rabbit blood with on-line microdialysis sampling.

Sensitive detection of endonuclease activity and inhibition using gold nanorods.

A novel plant tissue-based chemiluminescence (CL) biosensor for glycolic acid combined with flow injection analysis is proposed in this paper The spinach tissue acts as the molecular recognition e

Plant tissue-based chemiluminescence flow biosensor for glycolic acid.

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