Hybridization Of Complementary DNA Research Articles

Integrated Rayleigh wave streaming-enhanced sensitivity of shear horizontal surface acoustic wave biosensors

Shear horizontal surface acoustic wave (SH-SAW) sensors are regarded as a promising alternative for label-free, sensitive, real time and low-cost detection. Nevertheless, achieving high sensitivity with SH-SAW has approached its limit imposed by the mass transport and probe-target affinity. We present here an SH-SAW biosensor accompanied by a unique Rayleigh wave-based actuator. The platform assembled on an ST-quartz substrate consists of dual-channel SH-SAW delay lines fabricated along a 90°-rotated direction, whilst another interdigital electrode (IDT) is orthogonally placed to generate Rayleigh waves so as to induce favourable streaming in the bio-chamber, enhancing the binding efficiency of the bio-target. Theoretical foundation and simulation have shown that Rayleigh acoustic streaming generates a level of agitation that accelerates the mass transport of the biomolecules to the surface. A fourfold improvement in sensitivity is achieved compared with conventional SH-SAW biosensors by means of complementary DNA hybridization with the aid of the Rayleigh wave device, giving a sensitivity level up to 6.15 Hz/(ng/mL) and a limit of detection of 0.617 ng/mL. This suggests that the proposed scheme could improve the sensitivity of SAW biosensors in real-time detection.

Dual-mode electrochemical/colorimetric microfluidic sensor integrated tetrahedral DNA nanostructures with Au/Ni-Co LDH NCs nanozyme for ultrasensitive detection of aflatoxin B1

Aflatoxin B1 (AFB1) is one of the most hazardous mycotoxins and lead to a deadly danger to animal and human health. The development of portable, low-cost, and easy to operate analytical tools is essential for AFB1 detection, especially in resource-limited regions. Herein, a dual-mode microfluidic paper-based analytical device (μPAD) with electrochemical and colorimetric readout was constructed for AFB1 detection using Au NPs anchored Ni-Co layered double hydroxides nanocages (Au/Ni-Co LDH NCs) as a signal amplifier. In this design, tetrahedral DNA nanostructures (TDNs) were employed as a scaffold to anchor “bottom-up” aptamers (Apt) for improving capture efficiency of AFB1. Au/Ni-Co LDH NCs with excellent peroxidase (POD)-like activity were bound on the TDNs through hybridization of Apt and complementary DNA (cDNA), a significant electrochemical signal of H2O2 reduction was generated. Meanwhile, the·OH from H2O2 decomposition catalyzed the oxidation of 3,3′,5,5′-tetramethylbenzidine and resulted in a colorimetric signal. The binding of target AFB1 to Apt triggered the dissociation of Apt/cDNA, causing the release of the signal amplifier from the sensing interface and signal decrease. Consequently, a detection range of 0.2 pg/mL-100 ng/mL for electrochemical and 50 pg/mL-100 ng/mL for colorimetric were achieved for AFB1, holding promising application in the fields of food safety.

Whispering Gallery Mode Microresonator Sensor Integrated in Exposed Core Fiber for Label-Free DNA Hybridization Detection

A novel optical fiber sensor using exposed-core fiber (ECF) to excite whispering gallery modes (WGMs) within a high refractive index barium titanate glass microsphere is proposed for achieving label-free real-time specific DNA detection. The microsphere is encapsulated into the exposed channel of the ECF allowing for physical stability while excited WGMs via the evanescent field. The structure enables the sensing area to be exposed to a large amount of aqueous solution and better contact with the sample to be analyzed. Using a transmission measurement, a high Q-factor in the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> is obtained in an aqueous environment. To the best of our knowledge, this is the best Q-factor level obtained by the in fiber WGM sensor in an aqueous environment. Specific sequences of probe DNA are then bound to the surface of the microsphere so that specific detection of complementary DNA can be realized by tracking the wavelength shift the WGM resonance. Experimental results show a red shift of 5.6 pm for complementary DNA hybridization detection and less than 1 pm fluctuation for non-complementary DNA detection. The portable integrated sensor with miniature size has great potential for aqueous environmental sensing applications in the fields of diseases diagnostics, chemical analysis, and environmental protection.

Self-calibrated magnetic aptamer sensor with dual Lanthanide-assisted Time-resolved luminescence for high-sensitive detection of melanoma exosomal PD-L1

Highly sensitive detection of melanoma-derived exosomal PD-L1 plays a key role in non-invasive diagnosis of melanoma. Here, we proposed a self-calibrated magnetic aptamer sensor (sCMAS) for sensitive detection of melanoma exosomal PD-L1, using the dual lanthanide-assisted luminescence as well as the ratiometric fluorescent probe strategy to overcome limitations caused by systematic or environmental factors, thereby providing a more stable and liable detection output. Generally, the sCMAS employs the Tb-based nanoparticles (TbNps), which were immobilized on magnetic Fe3O4 microparticles, for stable luminescent reference signal report and the BHHCT-Eu3+ complex for detection signal report of the specific exosomal PD-L1 recognition. Particularly, the dual time-resolved luminescent elements were bridged through the PD-L1-responsive aptamer and its complementary DNA hybridization chain. Recognition of exosomes with the aptamer expelled the detection signal (BHHCT-Eu3+) only, leading to an exosome concentration-dependent liner increase of reference signal/detection signal ratio value in a broad concentration range (1.05 × 105–1.05 × 1010 particles/mL), and an extremely low calculated detection limitation of 1.88 × 102 particles/mL. Further, sCMAS allowed a rapid and efficient differentiation of the health samples from melanoma samples, even those early metastatic melanoma cases. Promisingly, this sCMAS developed in this work would provide a vast opportunity for future evaluation of tumor markers (exosomes, cells, proteins, etc.), and will provide a powerful tool in liquid biopsies.

Development of a label-free electrochemical aptasensor for ultrasensitive detection of ochratoxin A

The prevalent ochratoxin A (OTA) contamination in food has increased the urgency to develop sensitive and accurate detection methods. This study reported a conveniently fabricated label-free electrochemical (EC) aptasensor for ultrasensitive detection of OTA based on the competitive binding of OTA with its specific aptamer without any signal amplification strategy. A gold electrode (AuE) was modified with a compact layer of double-stranded DNA (dsDNA), obtained via OTA aptamer and complementary DNA (cDNA) hybridization, to act as a barrier for redox probe [Fe(CN) 6 ] 3-/4- to AuE access. This led to a high initial electron-transfer resistance (R ct ), recorded via electrochemical impedance spectroscopy (EIS). Since the aptamer displayed a higher affinity to OTA than cDNA, the added OTA triggered aptamer dissociation from AuE to form the OTA-aptamer complex, obviously decreasing the R ct . The target-induced variation in the resistance response strongly depended on the OTA concentration. Optimum conditions improved the linear relationship between R ct and the logarithm of OTA concentration in a range of 0.05–10 ng/mL with a limit of detection (LOD) of 0.05 ng/mL for OTA. Recoveries of 74.8–105% with relative standard deviations (RSDs) of 8.86–13.09% were obtained in the spiked malt samples. The Real-world detection of OTA in the actual malt samples confirmed the reliability of the convenient, cost-effective, and highly specific impedimetric aptasensor, exhibiting significant promise for extended application in food control to identify more hazardous contaminants by altering the corresponding aptamers. • A label-free electrochemical impedimetric aptasensor for OTA detection was developed. • No extra coupling medium was involved for immobilizing the aptamers. • The aptasensor achieved high sensitivity for OTA without signal amplification. • The impedimetric aptasensor succeeded in real malt samples with satisfactory recoveries. • The aptasensor can be extended to more contaminants in foods via replacing the corresponding aptamers.

DNA-Modified Liquid Crystal Droplets.

In this work, we have combined the advantages of sequence programmability of DNA nanotechnology and optical birefringence of liquid crystals (LCs). Herein, DNA amphiphiles were adsorbed onto LC droplets. A unique phenomenon of LC droplet aggregation was demonstrated, using DNA-modified LC droplets, through complementary DNA hybridization. Further functionalization of DNA-modified LC droplets with a desired DNA sequence was used to detect a wide range of chemicals and biomolecules, such as Hg2+, thrombin, and enzymes, through LC droplet aggregation and vice versa, which can be seen through the naked eye. These DNA-modified LC droplets can be printed onto a desired patterned surface with temperature-induced responsiveness and reversibility. Overall, our work is the first to report DNA-modified LC droplet, which provides a general detection platform based on the development of DNA aptamers. Additionally, this work inspires the exploration of surface information visualization combined with microcontact printing.

Copolymer Coatings for DNA Biosensors: Effect of Charges and Immobilization Chemistries on Yield, Strength and Kinetics of Hybridization

The physical–chemical properties of the surface of DNA microarrays and biosensors play a fundamental role in their performance, affecting the signal’s amplitude and the strength and kinetics of binding. We studied how the interaction parameters vary for hybridization of complementary 23-mer DNA, when the probe strands are immobilized on different copolymers, which coat the surface of an optical, label-free biosensor. Copolymers of N, N-dimethylacrylamide bringing either a different type or density of sites for covalent immobilization of DNA probes, or different backbone charges, were used to functionalize the surface of a Reflective Phantom Interface multispot biosensor made of a glass prism with a silicon dioxide antireflective layer. By analyzing the kinetic hybridization curves at different probe surface densities and target concentrations in solution, we found that all the tested coatings displayed a common association kinetics of about 9 × 104 M−1·s−1 at small probe density, decreasing by one order of magnitude close to the surface saturation of probes. In contrast, both the yield of hybridization and the dissociation kinetics, and hence the equilibrium constant, depend on the type of copolymer coating. Nearly doubled signal amplitudes, although equilibrium dissociation constant was as large as 4 nM, were obtained by immobilizing the probe via click chemistry, whereas amine-based immobilization combined with passivation with diamine carrying positive charges granted much slower dissociation kinetics, yielding an equilibrium dissociation constant as low as 0.5 nM. These results offer quantitative criteria for an optimal selection of surface copolymer coatings, depending on the application.

Rapid and Sensitive Detection of Severe Acute Respiratory Syndrome Coronavirus 2 in Label-Free Manner Using Micromechanical Sensors.

Coronavirus (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been identified as a deadly pandemic. The genomic analysis of SARS-CoV-2 is performed using a reverse transcription-polymerase chain reaction (RT-PCR) technique for identifying viral ribonucleic acid (RNA) in infected patients. However, the RT-PCR diagnostic technique is manually laborious and expensive; therefore, it is not readily accessible in every laboratory. Methodological simplification is crucial to combat the ongoing pandemic by introducing quick, efficient, and affordable diagnostic methods. Here, we report how microcantilever sensors offer promising opportunities for rapid COVID-19 detection. Our first attempt was to capture the single-stranded complementary DNA of SARS-CoV-2 through DNA hybridization. Therefore, the microcantilever surface was immobilized with an oligonucleotide probe and detected using complementary target DNA hybridization by a shift in microcantilever resonance frequency. Our results show that microcantilever sensors can discriminate between complementary and noncomplementary target DNA on a micro to nanoscale. Additionally, the microcantilever sensors’ aptitude toward partial complementary DNA determines their potential to identify new variants of coronavirus. Therefore, microcantilever sensing could be a vital tool in the effort to extinguish the spreading COVID-19 pandemic.

Dynamic Shape Transformation of a DNA Scaffold Applied for an Enzyme Nanocarrier.

Structural programmability and accurate addressability of DNA nanostructures are ideal characteristics for the platform of arranging enzymes with the nanoscale precision. In this study, a three-dimensional DNA scaffold was designed to enable a dynamic shape transition from an open plate-like structure to its closed state of a hexagonal prism structure. The two domains in the open state were folded together to transform into the closed state by hybridization of complementary short DNA closing keys at both of the facing edges in over 90% yield. The shape transformation of the DNA scaffold was extensively studied by means of the fluorescence energy transfer measurement, atomic force microscope images, and agarose gel electrophoretic analyses. A dimeric enzyme xylitol dehydrogenase was assembled on the DNA scaffold in its open state in a high-loading yield. The enzyme loaded on the scaffold was subsequently transformed to its closed state by the addition of short DNA closing keys. The enzyme encapsulated in the closed state displayed comparable activity to that in the open state, ensuring that the catalytic activity of the enzyme was well maintained in the DNA nanocarrier. The nanocarrier with efficient encapsulation ability is potentially applicable for drug delivery, biosensing, biocatalytic, and diagnostic tools.

Enzyme-free and label-free detection of Staphylococcus aureus based on target-inhibited fluorescence signal recovery

In this work, a one-step fluorometric strategy based on nanometal surface energy transfer (NSET) between carbon dots (CDs) and gold nanoparticles (AuNPs) was developed for facile detection of Staphylococcus aureus (S. aureus). The fluorescence of CDs was quenched up to 63.5% by AuNPs due to nucleic acid hybridization in the presence of linker DNA, which contained the complementary sequences of S. aureus-specific aptamer, and the fluorescence signal was in the “off” state. Upon aptamer addition, the CDs was released from linker DNA through the strong competitiveness of aptamer, leading to the notable fluorescence recovered. Once S. aureus is introduced, aptamer preferentially bind to the bacterial surface and cannot hybridize with complementary sequences in the linker DNA, resulting in the fluorescence signal with “off” state. Based on these findings, the performance and reliability of the fluorescence-based assay were evaluated. Compared to direct hybridization of complementary DNA on the surface of CDs and AuNPs, our sensing strategy has enhanced detection limit (10 cfu⋅mL−1) and improved linear range (10 to 106 cfu⋅mL−1) for S. aureus. Therefore, our proposed enzyme-free and label-free strategy may become a promising method for ease of operation, sensitive and selective S. aureus detection.

Narrower Nanoribbon Biosensors Fabricated by Chemical Lift-off Lithography Show Higher Sensitivity.

Wafer-scale nanoribbon field-effect transistor (FET) biosensors fabricated by straightforward top-down processes are demonstrated as sensing platforms with high sensitivity to a broad range of biological targets. Nanoribbons with 350 nm widths (700 nm pitch) were patterned by chemical lift-off lithography using high-throughput, low-cost commercial digital versatile disks (DVDs) as masters. Lift-off lithography was also used to pattern ribbons with 2 μm or 20 μm widths (4 or 40 μm pitches, respectively) using masters fabricated by photolithography. For all widths, highly aligned, quasi-one-dimensional (1D) ribbon arrays were produced over centimeter length scales by sputtering to deposit 20 nm thin-film In2O3 as the semiconductor. Compared to 20 μm wide microribbons, FET sensors with 350 nm wide nanoribbons showed higher sensitivity to pH over a broad range (pH 5 to 10). Nanoribbon FETs functionalized with a serotonin-specific aptamer demonstrated larger responses to equimolar serotonin in high ionic strength buffer than those of microribbon FETs. Field-effect transistors with 350 nm wide nanoribbons functionalized with single-stranded DNA showed greater sensitivity to detecting complementary DNA hybridization vs 20 μm microribbon FETs. In all, we illustrate facile fabrication and use of large-area, uniform In2O3 nanoribbon FETs for ion, small-molecule, and oligonucleotide detection where higher surface-to-volume ratios translate to better detection sensitivities.

Tuning the dynamic range of an Au-nanoparticle-based DNA hybridization assay by optimizing particle size, concentration, and surface probe density

Our aim is to broaden the dynamic range of target DNA detection by an Au nanoparticle (AuNP) sandwich assay based on complementary DNA hybridization. We conducted electrophoresis band analysis for different sizes and concentrations of AuNPs bearing different numbers of surface-conjugated probe DNA molecules. We found that the AuNP concentration is critical to determining the maximum quantification limit (upper limit of the dynamic range). The number of immobilized probe DNAs per AuNP was also optimized to prevent errors in determining the target DNA concentration and to raise the upper limit. We examined AuNPs with diameters ranging from 15 to 40 nm at different concentrations and demonstrated tunability of the dynamic ranges spanning two to three orders of magnitude. The use of both 15 and 40 nm AuNPs can cover a dynamic range of over four orders of magnitude.

Ultrasensitive DNA biosensor for hepatitis B virus detection based on tin-doped WO3/In2O3 heterojunction nanowire photoelectrode under laser amplification.

The fabrication of a highly sensitive DNA biosensor based on tin-doped WO3/In2O3 nanowires as heterojunction photoelectrode for detection of hepatitis B virus is reported. The tin-doped WO3/In2O3 nanowires were fabricated via a physical vapor deposition mechanism and were nearly 50nm in width. The single-strand DNA probe was covalently immobilized on the nanowire surface. The biosensor could detect the hybridization of complementary DNA in a label-free approach at very low concentrations. The biodetection processes were conducted through reduction-oxidation reactions in the electrochemical impedance spectral measurements. The electrochemical impedance responses were biased under laser amplification to achieve the detection limit of 1fM. The fabricated biosensor could detect DNA concentrations from 0.1pM to 10μM linearly in the calibration plot. Due to laser amplification, more charged carriers were released and they interacted with DNA on the electrode surface. The efficiency of the charge transfer parameter was enhanced by a photogeneration process, and the electron-hole recombination rate could intensively increase biosensor sensitivity, selectivity, and distinguishability. The stability of the nanowire biosensor under laser amplification demonstrated 96% of its initial responses after 6weeks of maintenance. Graphical abstract.

GRNA Sequence Heterology Tolerance Catalyzed by CRISPR/Cas in an In Vitro Homology-Directed Repair Reaction

CRISPR and associated Cas nucleases are genetic engineering tools revolutionizing innovative approaches to cancer and inherited diseases. CRISPR-directed gene editing relies heavily on proper DNA sequence alignment between the guide RNA (gRNA)/CRISPR complex and its genomic target. Accurate hybridization of complementary DNA initiates gene editing in human cells, but inherent gRNA sequence variation that could influence the gene editing reaction has been clearly established among diverse genetic populations. As this technology advances toward clinical implementation, it will be essential to assess what degree of gRNA variation generates unwanted and erroneous CRISPR activity. With the use of a system in which a cell-free extract catalyzes nonhomologous end joining (NHEJ) and homology-directed repair (HDR), it is possible to observe a more representative population of all forms of gene editing outcomes. In this manuscript, we demonstrate CRISPR/Cas complexation at heterologous binding sites that facilitate precise and error-prone HDR. The tolerance of mispairing between the gRNA and target site of the DNA to enable HDR is surprisingly high and greatly influenced by polarity of the donor DNA strand in the reaction. These results suggest that some collateral genomic activity could occur at unintended sites in CRISPR-directed gene editing in human cells.

Label-free discrimination of single nucleotide changes in DNA by reflectometric interference Fourier transform spectroscopy

Phenotypic variation – such as disease susceptibility and differential drug response – has a strong genetic component. Substantial effort has therefore been made to identify causal genomic variants explaining such variation among humans. Point mutations (PMs), which are single nucleotide changes in the genome, have been identified to be the most abundant form of causal genomic variants, making them useful, reliable diagnostic markers. Methods developed to genotype PMs have moved towards solid-phase assays, which not only show greater sensitivity and specificity, but also enable scalability and faster processing time. Most current assays are, however, based on fluorescent probes, which makes them relatively expensive. To develop a more cost-effective label-free genotyping method, we used a porous silicon (PSi) base as an efficient support for DNA biosensing and coupled it with reflectometric interference Fourier transform spectroscopy (RIFTS). To assess the versatility of this approach, we tested both a single nucleotide substitution in VKORC1 (-1639G > A; rs9923231) and a single nucleotide insertion in BRCA1 (5382insC; rs80357906). We demonstrate that the PSi-RIFTS method can efficiently detect both PM types with high sensitivity where hybridization of complementary DNA can be quantifiably differentiated from mismatch and non-complementary hybridization events. In addition, we show that the PSi base with immobilized DNA not only can be re-used to type further samples, but it also remains stable for 14 days, suggesting its potential for high-throughput applications.

Aptamer Structure Switch Fluorescence Anisotropy Assay for Small Molecules Using Streptavidin as an Effective Signal Amplifier Based on Proximity Effect.

Fluorescence polarization/anisotropy (FP/FA) approaches are appealing for targets sensing in homogeneous solution due to simplicity, reproducibility and sensitivity. Taking advantage of aptamers, aptamer structure switch FA methods are unique for small molecule detection based on the competition between aptamer-target binding and the hybridization of aptamer and complementary DNA (cDNA). However, usually small FA change is generated in these aptamer assays that only rely on size change caused by hybridization of an oligonucleotide because of the rapid local rotation of fluorophores and small mass change. Here we describe a simple and general aptamer structure switch FA assay for small molecules by employing a large-sized streptavidin (SA) as an effective signal amplifier based on proximity effect to reduce local rotation of fluorophore. In this design, the SA-labeled cDNA hybridizes with fluorescein (FAM)-labeled aptamer, drawing FAM close to SA and bringing a much higher FA value due to restricted local rotation of FAM. Small molecule-aptamer probe binding causes displacement of the SA-labeled cDNA and great decrease of FA. The closeness of SA to FAM in the duplex is key for this proposed strategy to produce large FA changes in target detection. Our method enabled to detect 60 pM aflatoxin B1 (AFB1), 1 nM ochratoxin A (OTA), and 0.5 μM adenosine triphosphate (ATP), respectively. This aptamer FA method combines the merits of aptamers and FA analysis, and it is promising in applications of detection of small molecules with good sensitivity.

H2O2 biosensor consisted of hemoglobin-DNA conjugate on nanoporous gold thin film electrode with electrochemical signal enhancement

In this research, we developed electrochemical biosensor which was composed of hemoglobin (Hb)-DNA conjugate on nanoporous gold thin film (NPGF) for hydrogen peroxide (H2O2) detection. For the first time, Hb and DNA was conjugated as a sensing platform for uniform orientation of Hb on electrode. The newly developed Hb-DNA conjugate was designed to prevent Hb from aggregation on electrode. DNA hybridization of Hb-DNA conjugate and complementary DNA (cDNA) on NPGF electrode induced uniformly assembled biosensor. Furthermore, NPGF electrode fabrication method was introduced to the increment of the surface area. To confirm the conjugation of Hb-DNA conjugate, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and ultraviolet–visible spectroscopy (UV–VIS) were used. Formation of the NPGF electrode was verified by scanning electron microscope (SEM). Atomic force microscopy (AFM) was operated for the confirmation of Hb-DNA immobilization on electrode. The electrochemical property of fabricated electrode was investigated by cyclic voltammetry (CV). Also, H2O2 sensing performance of fabricated electrode was investigated by amperometric i-t curve technique. This sensor showed a wide linear range from 0.00025 to 5.00 mM and a correlation coefficient of R2 = 0.9986. The detection limit was 250 nM. Proposed biosensor can be utilized as a sensing platform for development of biosensor.

Nano-assembly and welding of gold nanorods based on DNA origami and plasmon-induced laser irradiation

The bottom-up organization of noble metal nanostructures with nanometer-scale precision is an important goal in nanotechnology. Owing to their unique localized surface plasmon resonance, well-defined metal nanostructures arrays could be used to develop applications in nano-photonics, nano-plasmonics, and nano-electronics. This article proposes an alternative pathway of a controllable approach to assemble and weld together the gold nanostructures. As a typical plasmonic nanostructure, the gold nanorods (Au NRs) was synthesized by the classical seed-mediated growth method. Based on the recognition of biomolecules through complementary DNA hybridization, we used DNA origami strategy for controllable assembly of Au NRs. Rectangular DNA origami as a template can induce the geometrically assembled of Au NRs. We designed and fabricated tip-to-tip Au NRs dimers on the DNA templates. Then,the follow-up formation of nanojunctions between assembled tip-to-tip Au NRs dimers Au NRs was conducted by irradiating infrared femtosecond pulses laser. The ability to coupling plasmonic nanostructures by assembly and nano-welding could be fundamental to developing novel optical properties and ensuring materials.

Selective capture and sensitive fluorometric determination of Pseudomonas aeruginosa by using aptamer modified magnetic nanoparticles.

A fluorometric assay is described for the detection of the food pathogen Pseudomonas aeruginosa (P. aeruginosa). It is based on the hybridization of aptamer and fluorescein-labeled complementary DNA (FAM-cDNA) in combination with magnetic separation. In the absence of P. aeruginosa, FAM-cDNA is assembled on the surface of aptamer modified magnetic particles (MNPs) via hybridization between aptamer and cDNA. Upon addition of P. aeruginosa, FAM-cDNA is replaced by the bacteria and released from the MNPs since the aptamer preferentially binds to bacteria. After magnetic separation, the amount of bacteria can be quantified by determination of the fluorescence intensity (λexc/em = 494/525nm) of the supernatant containing the released FAM-cDNA. This kind of assay allows for both selective enrichment and sensitive fluorometric determination of bacteria in a single step. The assay has a response to the logarithm of P. aeruginosa concentration that is linearin the range between 10 and 108cfu·mL-1, with a detection limit as low as 1cfu·mL-1. The detection process can be finished within <1.5h. The feasibility of the assay was verified by detecting P. aeruginosa in spiked food samples. Graphical abstract Hybridization of aptamer and carboxyfluorescein labeled complementary DNA is combined with magnetic separation for detection of as low as 1cfu·mL-1 Pseudomonas aeruginosa. This kind of assay allows for both selective enrichment and sensitive fluorometric determination of bacteria in a single step.

Spiky gold shells on magnetic particles for DNA biosensors

Combined separation and detection of biomolecules has the potential to speed up and improve the sensitivity of disease detection, environmental testing, and biomolecular analysis. In this work, we synthesized magnetic particles coated with spiky nanostructured gold shells and used them to magnetically separate out and detect oligonucleotides using SERS. The distance dependence of the SERS signal was then harnessed to detect DNA hybridization using a Raman label bound to a hairpin probe. The distance of the Raman label from the surface increased upon complementary DNA hybridization, leading to a decrease in signal intensity. This work demonstrates the use of the particles for combined separation and detection of oligonucleotides without the use of an extrinsic tag or secondary hybridization step.