Stimuli responsive release of metalic nanoparticles on semiconductor substrates

Optically active metal nanoparticles have been of recent and broad interest for applications to biomarker detection because of their ability to enable high sensitivity enhancements in various optical detection techniques. Here, we report stimuli responsive release of metallic nanoparticles on a semiconductor thin film array structure based on pH change. The metallic nanoparticles are obtained by a simple redox procedure on the semiconductor surface. This approach allows controlling nanoparticle surface coatings in situ for biomolecule conjugation, such as DNA probes on nanoparticles, and rapid stimuli responsive release of these nanoparticles upon pH change.     

Comparison of infrared-excited up-converting phosphors and europium nanoparticles as labels in a two-site immunoassay

Research in the field of immunoassays and labels used in the detection has been recently focused on particulate reporters, which possess very high specific activity that excludes the label as a sensitivity limiting factor. However, the large size and shape of the particulate labels may produce additional problems to immunoassay performance. The aim of this work was to study with two identical non-competitive two-site immunoassays whether up-converting phosphor (UCP) particles are comparable in performance with europium(III) chelate-dyed nanoparticles as particulate labels. In addition we strived to verify the common assumption of the photostability of up-converting phosphor particles supporting their potential applicability in imaging. Detection limits in two-site immunoassay for free prostate-specific antigen (free-PSA) were 0.53 ng L⁻¹ and 1.3 ng L⁻¹ using two different up-converting phosphors and 0.16 ng L⁻¹ using europium(III) nanoparticle. Large size distribution and non-specific binding of up-converting phosphor particles caused assay variation in low analyte concentrations and limited the analytical detection limit. The non-specific binding was the major factor limiting the analytical sensitivity of the immunoassay. The results suggests the need for nanoscaled and uniformely sized UCP-particles to increace the sensitivity and applicability of up-converting phosphor particles. Anti-Stokes photoluminescence of up-converting phosphor particles did not photobleach when measured repeatedly, on the contrary, the time-resolved fluorescence of europium nanoparticles photobleached relatively rapidly.     

Optical single-particle detection in nanoholes towards simple parallel detection of molecular binding events

A novel scheme for the optical detection of a few or even single gold nanoparticle labels is introduced. It utilizes sub-wavelength holes in a chromium layer on a glass substrate, where a bioaffinity reaction could take place and the outcome (regarding particle label binding) can be monitored using optical means. Experiments in combination with simulations demonstrate that the presence of particles in such a chromium hole can be simply detected by using the color information of images by a charge couple device (CCD) camera without the need for additional spectroscopy setups. The presence of gold nanoparticles leads to a detectable red-shift in the images of the respective nanohole, which is the sensing principle of the sensor.     

Organometallic derivatizing agents in bioanalysis

Over the last few decades, the development of several innovative hyphenated analytical techniques and their routine use in laboratories has led to new possibilities for the quantitative analysis of biomolecules. Today, the identification and quantification of biomolecules such as peptides and proteins are essential to answer important medical, pharmaceutical, and biological questions. To allow efficient detection and structure elucidation of biomolecules, several approaches including derivatization strategies were investigated and applied during recent years. This article summarizes the current approaches for labeling and presents the different types of organometallic derivatizing agents used as labels. Furthermore, their analytical potential with respect to quantification and structure elucidation for different applications in the field of bioanalysis is discussed.     

Biomolecule induced nanoparticle aggregation: effect of particle size on interparticle coupling

Gold nanoparticles of variable sizes have been prepared by reducing HAuCl(4) with trisodium citrate by Frens' method. It has been found that the gold particles under consideration produce well-ordered aggregates upon interaction with a biomolecule, glutathione in variable acidic pH condition and exhibit pronounced changes in their optical properties arising due to electromagnetic interaction in the close-packed assembly. The effect of nanoparticle size on the nature of aggregation as well as the variation in the optical response due to variable degree of interparticle coupling effects amongst the gold particles have been investigated. The optical properties of the gold aggregates have been accounted in the light of Maxwell-Garnett effective medium theory considering the changes in the filling factor in different aggregates produced by variable sizes of gold colloids. The aggregates have been characterized by UV-vis spectroscopy, FTIR, Raman, XRD and TEM studies. It has been observed that a new peak appearing at a longer wavelength intensifies and shifts further to the red from the original peak position depends on the particle size, concentration of glutathione and pH of the solution. On the basis of the first appearance of a clearly defined new peak at longer wavelength, a higher sensitivity of glutathione detection has been achieved with gold nanoparticles of larger dimension.     

Nanomaterials in fluorescence-based biosensing

Fluorescence-based detection is the most common method utilized in biosensing because of its high sensitivity, simplicity, and diversity. In the era of nanotechnology, nanomaterials are starting to replace traditional organic dyes as detection labels because they offer superior optical properties, such as brighter fluorescence, wider selections of excitation and emission wavelengths, higher photostability, etc. Their size- or shape-controllable optical characteristics also facilitate the selection of diverse probes for higher assay throughput. Furthermore, the nanostructure can provide a solid support for sensing assays with multiple probe molecules attached to each nanostructure, simplifying assay design and increasing the labeling ratio for higher sensitivity. The current review summarizes the applications of nanomaterials—including quantum dots, metal nanoparticles, and silica nanoparticles—in biosensing using detection techniques such as fluorescence, fluorescence resonance energy transfer (FRET), fluorescence lifetime measurement, and multiphoton microscopy. The advantages nanomaterials bring to the field of biosensing are discussed. The review also points out the importance of analytical separations in the preparation of nanomaterials with fine optical and physical properties for biosensing. In conclusion, nanotechnology provides a great opportunity to analytical chemists to develop better sensing strategies, but also relies on modern analytical techniques to pave its way to practical applications.

Nanoparticle-based immunosensors and immunoassays for aflatoxins

Aflatoxins are naturally existing mycotoxins produced mainly by Aspergillus flavus and Aspergillus parasiticus, present in a wide range of food and feed products. Because of their extremely high toxicity and carcinogenicity, strict control of maximum residue levels of aflatoxins in foodstuff is set by many countries. In daily routine, different chromatographic methods are used almost exclusively. As supplement, in several companies enzyme immunoassay-based sample testing as primary screening is performed. Recently, nanomaterials such as noble metal nanoparticles, magnetic particles, carbon nanomaterials, quantum dots, and silica nanomaterials are increasingly utilized for aflatoxin determination to improve the sensitivity and simplify the detection. They are employed either as supports for the immobilization of biomolecules or as electroactive or optical labels for signal transduction and amplification. Several nanoparticle-based electrochemical, piezoelectric, optical, and immunodipstick assays for aflatoxins have been developed. In this review, we summarize these recent advances and illustrate novel concepts and promising applications in the field of food safety.     

Magnetic nanoparticles in microfluidic and sensing: From transport to detection

Superparamagnetic nanoparticles are attracting significant attention. Therefore, being explored in microsystems for a wide range of applications. Typical examples include lab-on-a-chip and microfluidics for synthesis, detection, separation, and transportation of different bioanalytes, such as biomolecules, cells, and viruses to develop portable, sensitive, and cost-effective biosensing systems. Particularly, microfluidic systems incorporated with magnetic nanoparticles and, in combination with magnetoresistive sensors, shift diagnostic and analytical methods to a microscale level. In this context, nanotechnology enables the miniaturization and integration of a variety of analytical functions in a single chip for manipulation, detection, and recognition of bioanalytes reliably and flexibly. In consideration of the above, recent development and benefits are elaborated herein to discuss the role of magnetic nanoparticles inside the microchannels to design highly efficient disposable point-of-care applications from transportation to the detection of bioanalytes.     

Carbon nanomaterials and metallic nanoparticles-incorporated electrochemical sensors for small metabolites: Detection methodologies and applications

Detection of small metabolite biomarkers at different concentrations could be powerfully used for disease diagnosis and progression. To enhance detection capabilities, nanomaterials possessing excellent optical and electrochemical properties have been integrated into a wide range of sensing or detection platforms. This review will highlight recent developments in creating electrochemical sensors alongside biosensors using carbon nanomaterials and metallic nanoparticles that target small metabolites. Moreover, electrochemical sensors having different detection strategies toward metabolites (such as amino acids, amino acid–derived neurotransmitters, vitamins, adenosine triphosphate, and purine derivatives) will be discussed. Finally, certain challenging issues and future aspects of nanomaterials-integrated electrochemical sensors for small metabolites will be discussed.     

Semiconductor quantum dots for bioanalysis

Semiconductor nanoparticles, or quantum dots (QDs), have unique photophysical properties, such as size-controlled fluorescence, have high fluorescence quantum yields, and stability against photobleaching. These properties enable the use of QDs as optical labels for the multiplexed analysis of immunocomplexes or DNA hybridization processes. Semiconductor QDs are also used to probe biocatalytic transformations. The time-dependent replication or telomerization of nucleic acids, the oxidation of phenol derivatives by tyrosinase, or the hydrolytic cleavage of peptides by proteases are probed by using fluorescence resonance energy transfer or photoinduced electron transfer. The photoexcitation of QD-biomolecule hybrids associated with electrodes enables the photoelectrochemical transduction of biorecognition events or biocatalytic transformations. Examples are the generation of photocurrents by duplex DNA assemblies bridging CdS NPs to electrodes, and by the formation of photocurrents as a result of biocatalyzed transformations. Semiconductor nanoparticles are also used as labels for the electrochemical detection of DNA or proteins: Semiconductor NPs functionalized with nucleic acids or proteins bind to biorecognition complexes, and the subsequent dissolution of the NPs allows the voltammetric detection of the related ions, and the tracing of the recognition events.     

Sandwich-type immunosensors and immunoassays exploiting nanostructure labels: A review

Methods based on sandwich-type immunosensors and immunoassays have been developed for detection of multivalent antigens/analytes with more than one eptiope due to the use of two matched antibodies. High-affinity antibodies and appropriate labels are usually employed for the amplification of detectable signal. Recent research has looked to develop innovative and powerful novel nanoparticle labels, controlling and tailoring their properties in a very predictable manner to meet the requirements of specific applications. This articles reviews recent advances, exploiting nanoparticle labels, in the sandwich-type immunosensors and immunoassays. Routine approaches involve noble metal nanoparticles, carbon nanomaterials, semiconductor nanoparticles, metal oxide nanostructures, and hybrid nanostructures. The enormous signal enhancement associated with the use of nanoparticle labels and with the formation of nanoparticle-antibody-antigen assemblies provides the basis for sensitive detection of disease-related proteins or biomolecules. Techniques commonly rely on the use of biofunctionalized nanoparticles, inorganic-biological hybrid nanoparticles, and signal tag-doped nanoparticles. Rather than being exhaustive, this review focuses on selected examples to illustrate novel concepts and promising applications. Approaches described include the biofunctionalized nanoparticles, inorganic-biological hybrid nanoparticles, and signal tage-doped nanoparticles. Further, promising application in electrochemical, mass-sensitive, optical and multianalyte detection are discussed in detail.     

Noncovalent labeling of biomolecules with red and near- infrared dyes

Biopolymers such as proteins and nucleic acids can be labeled with a fluorescent marker to allow for their detection. Covalent labeling is achieved by the reaction of an appropriately functionalized dye marker with a reactive group on a biomolecule. The recent trend, however, is the use of noncovalent labeling that results from strong hydrophobic and/or ionic interactions between the marker and biomolecule of interest. The main advantage of noncovalent labeling is that it affects the functional activity of the biomolecule to a lesser extent. The applications of luminescent cyanine and squarylium dyes are reviewed.     

水分散性硫化镉纳米粒子的制备研究进展

表面修饰的硫化镉纳米粒子荧光性能优异而稳定,激发光谱宽,发射光谱窄而对称且发射波长可通过改变材料的粒径大小和组成来调控,因而在生物样本尤其是活组织的多色成像中极为有用,能有效避免因样本自身发光和光散射导致的信号干扰。硫化镉纳米粒子的研究已被许多科研工作者所青睐,是目前热点研究领域之一。近年来,水分散性硫化镉纳米粒子作生物荧光标记物的研究取得了长足的进展。本文综述了水分散性硫化镉纳米粒子的制备方法研究进展,分析了各种制备方法的优点与不足之处。     

Chemical sensing and imaging with metallic nanorods

In this Feature Article, we examine recent advances in chemical analyte detection and optical imaging applications using gold and silver nanoparticles, with a primary focus on our own work. Noble metal nanoparticles have exciting physical and chemical properties that are entirely different from the bulk. For chemical sensing and imaging, the optical properties of metallic nanoparticles provide a wide range of opportunities, all of which ultimately arise from the collective oscillations of conduction band electrons ("plasmons") in response to external electromagnetic radiation. Nanorods have multiple plasmon bands compared to nanospheres. We identify four optical sensing and imaging modalities for metallic nanoparticles: (1) aggregation-dependent shifts in plasmon frequency; (2) local refractive index-dependent shifts in plasmon frequency; (3) inelastic (surface-enhanced Raman) light scattering; and (4) elastic (Rayleigh) light scattering. The surface chemistry of the nanoparticles must be tunable to create chemical specificity, and is a key requirement for successful sensing and imaging platforms.     

Engineered Nanomaterial Assisted Signal‐amplification Strategies for Enhancing Analytical Performance of Electrochemical Biosensors

The design and development of modern biosensors for sensitive and selective detection of various biomarkers is important in diversified arenas including healthcare, environment, and food industries etc. The requirement of more robust and reliant biosensors lead to the development of various sensing modules. The nanomaterials having specific optical, electrical, and mechanical strength can pave the way towards development of ultrafast, robust, and miniaturized modules for biosensors. It can provide not only the point‐of‐care applicability but also has tremendous commercial as well as industrial justification. In order to improve the performance of the sensor systems, various nanostructure materials have been readily studied and applied for development of novel biosensors. In the last few years, researchers are engaged on harnessing the unique atomic and molecular properties of advance‐engineered materials including carbon nanotubes, graphene nanosheets, metal nanoparticles, metal oxide nanoparticles, and their nano‐conjugates. In view of such recent developments in nanomaterial engineering, the current review has been formulated emphasizing the role of these materials in surface engineering, biomolecule conjugation, and signal amplification for development of various ultrasensitive and robust biosensors having commercial as well as industrial viability. Attention is given on the electrochemical biosensors incorporating various nanomaterials and their conjugates. Importance of nanomaterials in the analytical performance of the various biosensor has also been discussed. To put a perceptive insights on the importance of various nanomaterials, an extended table is incorporated, which includes probe design, analyte, LOD, and dynamic range of various electrochemical biosensors.     

Nanomaterial Based Biosensors for Detection of Biomarkers of Exposure to OP Pesticides and Nerve Agents: A Review

Organophosphorus (OP) pesticides are primarily used as insecticides and chemical warfare agents worldwide. Due to their impact on the environment and health, it is important to develop prompt and accurate pesticide analysis method. This review addresses recent advances and new trends in nanotechnology‐based biosensors for biological monitoring of exposures to OP pesticides and nerve agents. In order to determine them, we have to find the corresponding biomarkers. In 1989, the national academy of sciences (NAS)divided biomarkers into the following three categories: biomarker of exposure, biomarker of effect and biomarker of susceptibility (Figure 1A). The unique chemical and physical properties of nanomaterial have paved the way to new and improved sensing devices, in general, and electrochemical/optical biosensors, in particular. In this paper, background information and a general overview of electrochemical/immunoassay detection techniques are provided. Various nanomaterial labels are discussed. Usually nanomaterials can be roughly divided into nanometer powder, nanometer fiber, nanometer film, nanometer block and so on four classes, such as colloidal gold, semiconductor nanoparticles and carbon nanomaterial (Figure 1B). In addition, we discuss some future considerations and opportunities for advancing the use of biosensors for environmental and health studies.     

Reactive and Highly Submicron Magnetic Latexes for Bionanotechnology Applications

Summary: Colloidal particles are largely used in biomedical applications as a solid support, as a carrier, as nanoreactors and as labels for target molecule detection. With the recent development of bionanotechnology, more appropriate colloidal particles should be elaborated. In this direction, new specification are listed in order to develop reactive nanoparticles to be use in microsystems, microfluids and all combined systems in which we can conduct sample preparation, specific capture, purification, concentration and detection in small volume (generally less than 100 µl). Then the aim of this short review is to give to the readers some recent orientations of reactive magnetic latex particles for in vitro bionanotechnology applications.     

Smart nano-architectures as potential sensing tools for detecting heavy metal ions in aqueous matrices

The discharge of heavy metal ions into water resources as a result of human activities has become a global issue. Contamination with heavy metal ions poses a major threat to the environment and human health. Therefore, there is a dire need to probe the presence of heavy metal ions in a more selective, facile, quick, cost-effective and sensitive way. Conventional sensors are being utilized to sense heavy metal ions; however, various challenges and limitations like interference, overlapping of oxidation potential, selectivity and sensitivity are associated with them that limit their in-field applicability. Hence, nanomaterial based chemical sensors have emerged as an alternative substitute and are extensively employed for the detection of heavy metal ions as a potent analytical tool. The incorporation of nanomaterials in sensors increases their sensitivity, selectivity, portability, on-site detection capability and device performance. Nanomaterial based electrodes exhibit enhanced performance because surface of electrode at nano-scale level offers high catalytic potential, large active surface area and high conductivity. Therefore, this review addresses the recent progress on chemical sensors based on different nanomaterials such as carbon nanotubes (CNTs), metal nanoparticles, graphene, carbon quantum dots and nanocomposites for sensing heavy metals ions using different sensing approaches. Furthermore, various types of optical sensors such as fluorescence, luminescence and colorimetry sensors have been presented in detail.     

Quantification of local hydration at the surface of biomolecules using dual-fluorescence labels

By using four labels of the 3-hydroxyflavone family displaying selective sensitivity to hydrogen bond (HB) donors and poor response to other polar molecules, we developed an approach for measuring local water concentration [H(2)O](L) (or partial volume of water: W(A) = [H(2)O](L)/55.6) in the label surrounding both in solvent mixtures and in biomolecules by the intensity ratio of two emissive forms of the label, N*/T*. Using a series of binary water/solvent mixtures with limited preferential solvation effects, a linear dependence of log(N*/T*) on the local concentration of HB donor was obtained and then used as a calibration curve for estimating the W(A) values in the surroundings of the probes conjugated to biomolecules. By this approach, we estimated the hydration of the labels in different peptides and their complexes with DNAs. We found that W(A) values for the label at the peptide N-terminus are lower (0.63-0.91) than for free labels and depend strongly on the nature of the N-terminal amino acid. When complexed with different DNAs, the estimated hydration of the labels conjugated to the labeled peptides was much lower (W(A) = 0-0.47) and depended on the DNA nature and linker-label structure. Thus, the elaborated method allows a site-specific evaluation of hydration at the surface of a biomolecule through the determination of the partial volume of water. We believe the developed procedure can be successfully applied for monitoring hydration at the surface of any biomolecule or nanostructure.     

Nanomaterial labels in electrochemical immunosensors and immunoassays

This article reviews recent advances in nanomaterial labels in electrochemical immunosensors and immunoassays. Various nanomaterial labels are discussed, including colloidal gold/silver, semiconductor nanoparticles, and markers loaded nanocarriers (carbon nanotubes, apoferritin, silica nanoparticles, and liposome beads). The enormous signal enhancement associated with the use of nanomaterial labels and with the formation of nanomaterial-antibody-antigen assemblies provides the basis for ultrasensitive electrochemical detection of disease-related protein biomarkers, biothreat agents, or infectious agents. In general, all endeavors cited here are geared to achieve one or more of the following goals: signal amplification by several orders of magnitude, lower detection limits, and detecting multiple targets.