Quantum Dot Biosensor Research Articles

Aptamer-Conjugated Quantum Dot Optical Biosensors: Strategies and Applications

Quantum dots (QDs) represent the promising new generation of luminophores owing to their size-, composition-, and surface-dependent tunable photoluminescence (PL) and photochemical stability. The development of various QD composites with high PL and good biocompatibility has facilitated the use of aptamer-functionalized QD biosensors for highly sensitive and specific detection of molecules in clinical and environmental settings. In addition to describing the recent advances in aptamer-based QD biosensor technology for the detection of diverse chemicals and biomolecules, this review provides recent examples of sensing strategies based on optical signal enhancement and quenching of QDs. It also discusses potential strategies for the development of biosensors to widen their practical applications across various scientific and technological fields.

Quantum dot biosensor combined with antibody and aptamer for tracing food-borne pathogens

Abstract Due to the increasing number of food-borne diseases, more attention is being paid to food safety. Food-borne pathogens are the main cause of food-borne diseases, which seriously endanger human health, so it is necessary to detect and control them. Traditional detection methods cannot meet the requirements of rapid detection of food due to many shortcomings, such as being time-consuming, laborious or requiring expensive instrumentation. Quantum dots have become a promising nanotechnology in pathogens tracking and detection because of their excellent optical properties. New biosensor detection methods based on quantum dots are have been gradually developed due to their high sensitivity and high specificity. In this review, we summarize the different characteristics of quantum dots synthesized by carbon, heavy metals and composite materials firstly. Then, attention is paid to the principles, advantages and limitations of the quantum dots biosensor with antibodies and aptamers as recognition elements for recognition and capture of food-borne pathogens. Finally, the great potential of quantum dots in pathogen detection is summarized.

SiRNA-directed self-assembled quantum dot biosensor for simultaneous detection of multiple microRNAs at the single-particle level

MicroRNAs are essential post-transcriptional regulators and may act as the noninvasive biomarkers for disease diagnosis. Sensitive and multiplexed detection of microRNAs may facilitate the accurate and early clinical diagnosis, but the available methods are usually compromised by using organic dyes as the signal probes, laborious chemical and enzymatic manipulations, and the complicated reaction schemes. Here we reported a siRNA-directed self-assembled quantum dot (QD) biosensor for facile and simultaneous detection of multiple microRNAs. In this biosensor, the binding of microRNA targets with corresponding QD nanoprobes leads to the formation of siRNA duplexes, which not only induces the spectrally resolved coding of microRNAs, but also facilitates the assembly of QDs:magnetic nanoparticle bioconjugates for the isolation and enrichment of target microRNAs. The disassembled QDs can be sensitively detected by single-molecule detection, enabling quantitatively sensing of microRNAs at the single-particle level. This biosensor employs only QDs as the signal reporters, which can simultaneously detect multiple microRNAs from the same sample and achieves femtomolar sensitivity and single-base mismatch selectivity without the involvement of any target labeling and amplification steps. Moreover, it can be successfully applied for simultaneous detection of circulating microRNAs in clinical serum samples, holding great potential in non-invasive early diagnosis and biomedical researches.

Impact of Antibody Bioconjugation on Emission and Energy Band Profile of CdSeTe/ZnS Quantum Dots

The variation of the photoluminescence (PL) and Raman scattering spectra of CdSeTe/ZnS quantum dots (QDs) on conjugation to an antibody has been investigated. Two types of CdSeTe/ZnS QD with different emission wavelength (705 nm and 800 nm) were studied comparatively before and after conjugation to anti-pseudorabies virus antibody (AB). Nonconjugated QDs were characterized by Gaussian-type PL bands. PL shifts to higher energy and asymmetric shape of PL bands was detected in PL spectra of bioconjugated QDs. The surface-enhanced Raman scattering effect was exhibited by the bioconjugated CdSeTe/ZnS QDs, indicating that the excitation light used in the Raman study generated electric dipoles in the AB molecules. The optical bandgap of the CdSeTe core was calculated numerically as a function of its radius based on an effective mass approximation model. The energy band diagrams for non- and bioconjugated CdSeTe/ZnS QDs were obtained, revealing a type II quantum well in the CdSeTe core. The calculations show that AB dipoles, excited in the bioconjugated QDs, stimulate a change in the energy band diagram of the QDs that alters the PL spectrum. These results could be useful for improving the sensitivity of QD biosensors.

Emission transformation in CdSe/ZnS quantum dots conjugated to biomolecules

The variation of photoluminescence (PL) spectra in CdSe/ZnS quantum dots (QDs) at the conjugation to antibodies (ABs) has been investigated and discussed in this paper. Two types of CdSe/ZnS QDs with different CdSe core sizes (5.4 and 6.4nm) and emissions (605 and 655nm) were studied before and after the conjugation to anti-Interleukin-10 (IL-10) and anti-Pseudo rabies virus (PRV) ABs. The PL high energy shift and asymmetric shape of PL bands have been detected in bioconjugated QDs. Note that the bioconjugation impact on spectral characteristics of CdSe/ZnS QD emission has been not studied yet in details. The surface enhanced Raman scattering (SERS) effect is revealed in bioconjugated CdSe/ZnS QDs. The SERS effect testifies that the excitation light used at the Raman study generates the electric dipoles in AB molecules. At the same time, the permanent position of LO-phonon Raman lines in Raman spectra of nonconjugated and bioconjugated QDs confirms that QD materials do not change at the bioconjugation. It is shown as well that the compressive strains do not play any role in the PL high energy shift in bioconjugated QDs. PL spectra of pure anti IL-10 ABs, anti PRV ABs, a phosphate buffer saline (PBS) and PL spectrum dependences versus excitation light intensities have been investigated as well. Finally, the PL spectrum transformation in bioconjugated QDs is attributed to varying the quantum confinement effect in CdSe/ZnS QDs and the energy band profiles in QD cores. Both these effects are stimulated by the electromagnetic field of excited AB dipoles. The obtained results can be useful for sensitivity improving the QD bio-sensors.

Electrocatalytic oxidation enhancement at the surface of InGaN films and nanostructures grown directly on Si(111)

Pronounced electrocatalytic oxidation enhancement at the surface of InGaN layers and nanostructures directly grown on Si by plasma-assisted molecular beam epitaxy is demonstrated. The oxidation enhancement, probed with the ferro/ferricyanide redox couple increases with In content and proximity of nanostructure surfaces and sidewalls to the c-plane. This is attributed to the corresponding increase of the density of intrinsic positively charged surface donors promoting electron transfer. Strongest enhancement is for c-plane InGaN layers functionalized with InN quantum dots (QDs). These results explain the excellent performance of our InN/InGaN QD biosensors and water splitting electrodes for further boosting efficiency.

Quantum-dot biosensor for hybridization and detection of R3500Q mutation of apolipoprotein B-100 gene.

A quantum-dot electrode system was developed as a transducer surface for covalent immobilization of a designed synthetic ApoB-100 specific probe, DNA hybridization and monitoring of DNA synthesis for the sensitive detection of R3500Q mutation of apolipoprotein B-100 (ApoB-100) gene. CdS-QDs cause an improvement in the fundamental characteristics of the electrode interface, such as its electroactive surface area, diffusion coefficient and electron transfer kinetics. The sensing characteristics of this biosensor offer a suitable potential for detection of target oligonucleotide with a detection limit of 3.4 × 10(-17)M. Also, the electrochemical responses of single-stranded DNA (ssDNA), DNA hybridization and DNA synthesis were investigated using electrochemical impedance spectroscopy (EIS). The extracted genomic DNA was detected based on changes in the charge transfer resistance (RCT) with [Fe(CN)6](3-/4-) as a redox probe. The proposed biosensor can distinguish between the normal sequence and the mutant sequence of ApoB-100 gene, promising a possibility to apply the QD-based biosensor for clinical investigations.

압타머 광학 바이오센서

In this review, we will discuss aptamer technologies including in vitro selection, signal transduction mechanisms, and designing aptamers and aptazyme for label-free biosensors and catalysts. Dye-displacement, a typical label-less method, is described here which allows avoiding relatively complex labeling steps and extending this application to any aptamers without specific conformational changes, in a more simple, sensitive and cost effective way. We will also describe most recent and advanced technologies of signaling aptamer and aptazyme for the various analytical and clinical applications. Quantum dot biosensor (QDB) is explained in detail covering designing and adaptations for multiplexed protein detection. Application to aptamer array utilizing self-assembled signaling aptamer DNA tile and the novel methods that can directly select smart aptamer or aptazyme experimentally and computationally will also be finally discussed, respectively.

Toward a solid-phase nucleic acid hybridization assay within microfluidic channels using immobilized quantum dots as donors in fluorescence resonance energy transfer

The optical properties and surface area of quantum dots (QDs) have made them an attractive platform for the development of nucleic acid biosensors based on fluorescence resonance energy transfer (FRET). Solid-phase assays based on FRET using mixtures of immobilized QD-oligonucleotide conjugates (QD biosensors) have been developed. The typical challenges associated with solid-phase detection strategies include non-specific adsorption, slow kinetics of hybridization, and sample manipulation. The new work herein has considered the immobilization of QD biosensors onto the surfaces of microfluidic channels in order to address these challenges. Microfluidic flow can be used to dynamically control stringency by adjustment of the potential in an electrokinetic-based microfluidics environment. The shearing force, Joule heating, and the competition between electroosmotic and electrophoretic mobilities allow the optimization of hybridization conditions, convective delivery of target to the channel surface to speed hybridization, amelioration of adsorption, and regeneration of the sensing surface. Microfluidic flow can also be used to deliver (for immobilization) and remove QD biosensors. QDs that were conjugated with two different oligonucleotide sequences were used to demonstrate feasibility. One oligonucleotide sequence on the QD was available as a linker for immobilization via hybridization with complementary oligonucleotides located on a glass surface within a microfluidic channel. A second oligonucleotide sequence on the QD served as a probe to transduce hybridization with target nucleic acid in a sample solution. A Cy3 label on the target was excited by FRET using green-emitting CdSe/ZnS QD donors and provided an analytical signal to explore this detection strategy. The immobilized QDs could be removed under denaturing conditions by disrupting the duplex that was used as the surface linker and thus allowed a new layer of QD biosensors to be re-coated within the channel for re-use of the microfluidic chip.

Green and Orange CdTe Quantum Dots as Effective pH-Sensitive Fluorescent Probes for Dual Simultaneous and Independent Detection of Viruses

One of the most highlighted and fastest moving interfaces of nanotechnology is the application of quantum dots (QDs) in biology. The unparalleled advantages of the size-tunable fluorescent emission and the simultaneous excitation at a single wavelength make QDs the great possibility for use in optical encoding detection. In this paper, we report that green and orange CdTe QDs as convenient, cheap, reversible, and effective pH-sensitive fluorescent probes could monitor the proton (H+) flux driven by ATP synthesis for dual simultaneous and independent detection of viruses on the basis of antibody-antigen reactions. A new kind of biosensor (consisting of the mixture of green-QDs-labeled chromatophores and orange-QDs-labeled chromatophores) fluorescent measurement system was established for rapid, simultaneous, and independent detection of two different kinds of viruses (i.e., H9 avian influenza virus and MHV68 virus). It is crucial to find that the green and orange QDs labeled biosensors coexisting in the detection system can work independently and do not interfere with each another in the fluorescence assays. In addition, a primary steady electric double layer (EDL) model for the QDs biosensors was proposed to illustrate the mechanism of simultaneous and independent detection of the biosensors. We believe that the pH-sensitive CdTe QDs based detection system, described in this paper, is an important step toward optical encoding and has a great potential for simultaneous and independent qualitative and quantitative multiple detection systems.