Magnetic Nanobeads Research Articles

Functional silica nanospheres for sensitive detection of H9N2 avian influenza virus based on immunomagnetic separation

Electrochemiluminescence (ECL) has been widely used in detection of biomarkers. However, the lacks of efficient ECL emitter and anti-interference ability limit its clinical application. Here, a sensitive ECL immunosensor was proposed for H9N2 avian influenza virus (H9N2 AIV) detection using functional silica nanospheres as signal carriers and magnetic nanobeads (MBs) as capture carriers. Functional silica nanospheres were prepared by encapsulating Ru(bpy)32+ in silica nanoparticles (RuSi NPs) followed by modifying with polyclonal antibody (pAb), amplifying the ECL signals by about 103-fold compared with the same concentration of Ru(bpy)32+. Targets could be directly captured and separated by MBs without sample pretreatment, which saved time and simplified operation. The integration of immunomagnetic separation improved the anti-interference ability, enabling the method feasible for practical applications. Based on functional silica nanospheres and MBs, the ECL immunosensor achieved ultrasensitive detection of 14 fg/mL H9N2 AIV with a dynamic range of 25 fg/mL to 25 ng/mL. Owing to its high sensitivity, good stability, selectivity, and anti-interference ability in complex samples through immunomagnetic separation, the method showed wonderful potential of application in clinical diagnosis.

A Novel Nanobead-Based Single-Molecule Pull-Down For Cell Populations and Single Cells

Conventional co-immunoprecipitation methods (co-IP/pull-down) commonly used for accessing protein-protein interactions (PPIs) require large numbers of cells and are thus unsuitable for studying PPIs in rare cells such as sensory hair cells, circulating tumor cells, and embryonic stem cells; this substantially hampers rare-cell research and therefore calls for the development of single-cell pull-down techniques. Equally important, such single-cell pull-down techniques enable investigation of cell-to-cell variation in PPIs. Recently, based on the principle of a published single-molecule pull-down assay (SiMPull), two single-cell pull-down techniques were developed. However, both methods present a considerably high technical barrier and can be applied only to very limited cell types such as bacteria or adherent cells and not to primary- or suspension-culture cells. Here, we report a highly innovative nanobead-based approach for SiMPull designed for cell populations and, more importantly, single cells. We used commercially available, pre-surface-functionalized magnetic nanobeads to capture the protein of interest together with its binding partners specifically from cell extracts and observed these interactions by fused fluorescent proteins or immunofluorescent labeling under microscope. For the single-cell SiMPull, we used microwell array chips to trap single cells and applied magnetic nanobeads to microwells. After cell lysis, the nanobeads captured target proteins and pulled them down to the glass bottom of the microwell upon imposing a magnetic field, followed by immunofluorescent labeling and visualization under microscope. Our methods are substantially simpler and faster than existing SiMPull techniques for cell populations and single cells and are considerably more widely applicable to all cell types. These two crucial features would enable universal application of our methods in common biological and clinical laboratories. The work was supported by Hong Kong RGC Grant GRF16111616.

Targeting of temozolomide using magnetic nanobeads: an in vitro study

Temozolomide, a chemotherapeutic drug that is often administered for the treatment of brain cancer has severe side effects and a poor aqueous solubility. In order to decrease the detrimental effect of the drug over healthy cells, a novel drug delivery vehicle was developed where the therapeutic drug was encapsulated within the hydrophobic cavities of b-CD modified magnetite nanoparticles, which are embedded in chitosan nanobeads prepared by salt addition. In-vitro studies have shown that the magnetic properties of the novel delivery vehicle are adequate for targeted drug delivery applications under an external magnetic field. Additionally, an increase in the amount of chitosan was shown to exhibit a strong shielding effect over the magnetic properties of the delivery vehicle, which lead to deterioration of the amount of captured drug at the targeted area, suggesting a delicate balance between the amounts of constituents composing the drug delivery vehicle.

Advances in Fully Automated Nucleic Acid Extraction System Based on Magnetic Nanobeads

Using magnetic nanobeads (MNBs) to extract nucleic acids is an efficient, inexpensive, easy automation, high throughput and good repeatability, instead of the traditional nucleic acid extraction (NAE) methods. Advances in fully automated MNBs-based nucleic acid extraction systems (MNAES) can push the frontiers of point-of-care testing (POCT) devices towards low-cost, automation, and enhanced accuracy molecular-level diagnostics. So, this paper introduces the pipettingbased MNAES with position of magnetic separation kit or tip, and based on magnetic bar MNAES with blending manner is shock or rotation. Further, advantages and disadvantages of various MNAES are compared. We envisage that the future trend in molecular diagnosis and monitoring will be facilitation, intelligent, miniaturization, and high throughput MNAES with sample-in-answer-out capability.

One-Step Monitoring of Multiple Enterovirus 71 Infection-Related MicroRNAs Using Core-Satellite Structure of Magnetic Nanobeads and Multicolor Quantum Dots.

The accurate and rapid monitoring of the expression levels of enterovirus 71 (EV71)-related microRNAs (miRNAs) can contribute to diagnosis of hand, foot, and mouth disease (HFMD) at the early stage. However, there is currently a lack of convenient methods for simultaneous monitoring of multiplex miRNAs in one step. Herein a one-step method for the simultaneous monitoring of multiple EV71 infection-related miRNAs is developed based on core-satellite structure assembled with magnetic nanobeads and quantum dots (MNs-ssDNA-QDs). In the presence of target miRNAs, duplex-specific nuclease (DSN)-assisted target recycling can be triggered, resulting in the release of QDs and recycling of target miRNAs. Then the simultaneous quantification can be easily realized by recording the corresponding amplified fluorescence signal of QDs in the suspension. With this method, simultaneous detection of hsa-miRNA-296-5p and hsa-miRNA-16-5p, potential biomarkers of EV71 infection, can be easily achieved with femtomolar sensitivity and single-base mismatch specificity. Moreover, the method is successfully used for monitoring of the expression level of miRNAs in EV71-infected cells at different time points, demonstrating the potential for diagnostic applications. With the merits of one-step operation and single-nucleotide mismatch discrimination, this work opens a new avenue for multiplex miRNAs detection. As different nucleotide sequences and multicolor QDs can be employed, this workis expected to offer great potentialfor the development of high throughput diagnosis.

Enrichment-Stowage-Cycle Strategy for Ultrasensitive Electrochemiluminescent Detection of HIV-DNA with Wide Dynamic Range.

Sensitive detection of human immunodeficiency virus DNA (HIV-DNA) is essential for timely diagnosis and cure of the illness. Herein, a novel "enrichment-stowage-cycle" strategy was proposed to fabricate a multiple amplified electrochemiluminecence (ECL) biosensor for HIV-DNA detection. On the basis of the enrichment role of magnetic nanobeads, assembly role of copolymer nanospheres and strand displacement amplification (SDA), the processes were named as "enrichment", "stowage", and "cycle", respectively. The method employed electrochemiluminescent nanospheres (ENs) as signal labels by assembling three layers of CdSe/ZnS quantum dots (QDs) onto the surface of copolymer nanospheres. Compared to QDs, the same concentration of ENs can the enhance the ECL intensity by about 11.3-fold. SDA could further amplify the signals by about 3.77-fold, possessing high sensitivity for low-abundant biomarkers detection. The integration of magnetic separation improved detection specificity and stability, making the method possible for practical application. On the basis of magnetic separation, ENs and SDA, the ECL biosensor realized ultrasensitive detection of 39.81 fM HIV-DNA, which was more sensitive than other HIV-DNA analytical methods, with a wide dynamic range of 0.05 pM to 50 nM. The successful detection of HIV-DNA in complex samples with good sensitivity and accuracy indicated its potential utilization in early judgment of diseases and fabrication of signal amplification platforms.

On-chip structure-switching aptamer-modified magnetic nanobeads for the continuous monitoring of interferon-gamma ex vivo

Cytokines are cell signaling molecules that indicate the health status of the body. In this study, we developed a microfluidic device integrated with structure-switching aptamers capable of continuously tracking the concentration of the cytokine interferon gamma (IFN-γ) in cell culture medium and blood serum. First, a ferrocene (Fc)-labeled structure-switching signaling aptamer with a hairpin structure targeting IFN-γ was immobilized on magnetic nanobeads by the strongest noncovalent interactions between streptavidin and biotin. The aptamer-modified magnetic nanobeads were trapped on a customized microfluidic chip by a magnetic field to form the sensing interface. The binding of IFN-γ could trigger the hairpin structure of the aptamer to unfold, pushing Fc redox molecules away from the sensing interface and consequently switching off the electrochemical signal. The change in the redox current of Fc was quantitatively related to the concentration of IFN-γ in a linear range of 10–500 pg mL−1 and with the lowest detection limit of 6 pg mL−1. This microfluidic device was specific to IFN-γ in the presence of overabundant serum proteins and allowed the continuous monitoring of IFN-γ without adding exogenous reagents. It provided a universal point-of-care biosensing platform for the real-time detection of a spectrum of analytes.

Effect of Spin Clustering on Basic and Relaxometric Properties of Magnetic Nanoparticles.

An increasing awareness about novel medical applications of smaller, inorganic-based nanoparticles, possessing unique properties at the nanoscale, has led to a burst of research activities in the development of "nanoprobes" for diagnostic medicine and agents for novel, externally activated therapies. In this research field magnetic nanoparticles are prominent due to fundamental peculiar properties particularly appealing for their use in materials and biomedical applications. Aiming to study the relationship between the topology of the magnetic nanoparticles and their efficacy as MRI contrast agents (relaxometric properties), we prepared three different stable colloidal suspension (ferrofluid) of magnetic nanobeads (MNBs) constituted by a discrete number of maghemite nanoparticles, arranged in disordered clusters or ordered in a polymeric matrix. An accurate morpho-dimensional and magnetic characterization displays the close correlation between the magnetic fundamental properties and the topology of our spin systems. The NMR relaxometry profiles confirmed the nature of the physical mechanisms inducing the increase of nuclear relaxation rates at low (magnetic anisotropy) and high (Curie relaxation) magnetic fields. Moreover the transverse relaxivity (r₂) values for all the MNBs are higher than those of common contrast agents and the differences between the three MNBs are suggested to be due to the spin topology effect.

Ursolic Acid Isolated from the Leaves of Loquat ( Eriobotrya japonica) Inhibited Osteoclast Differentiation through Targeting Exportin 5.

One of the conventional strategies for treating osteoporosis is to eliminate the multinucleated osteoclasts that are responsible for bone resorption. Our previous study revealed that ursolic acid, isolated from leaves of loquat that is used as tasty tea in Japan, suppressed osteoclastogenesis. We confirmed that ursolic acid exhibited osteoclast differentiation inhibitory activity with an 50% inhibitory concentration (IC50) value of 5.4 ± 0.96 μM. To disclose its mechanism of action, this study first uses polymer-coated magnetic nanobeads to identify potential target proteins. As a result, we identified a nuclear exporter protein named exportin 5 (XPO5). Further studies demonstrated that knockdown of XPO5 significantly blocks osteoclast differentiation ( P < 0.01). Expression profiling of mature microRNAs in the cells revealed that downregulation of XPO5 by small interfering RNA or by ursolic acid could downregulate the expression of mature microRNA let-7g-5p during osteoclast differentiation ( P < 0.01). Collectively, our findings suggest that ursolic acid inhibits osteoclast differentiation through targeting XPO5, which provides further evidence for the healthy function of the tea. This study also provides new insights into the role of XPO5 and its mediated microRNAs in treatment for bone resorption diseases.

Efficient recovery and enrichment of infectious rotavirus using separation with antibody-integrated graphite-encapsulated magnetic nanobeads produced by argon/ammonia gas plasma technology.

BackgroundRotavirus is the representative cause of severe acute gastroenteritis in young children. A characteristic feature of rotavirus is low infectious dose and robustness of the virion, suggesting sanitation and hygiene will have little impact. Thus, development of a vaccine should be given priority. Efficient capture of infectious viruses is an important step in generating a vaccine. Previously, antibody-integrated magnetic nanobeads (MNBs) have been developed for virus capture. This study examines the applicability of this method for infectious rotavirus recovery and enrichment.Materials and methodsGraphite-encapsulated MNBs were treated with radio frequency (RF) excited Ar/NH3 gas mixture plasma to introduce amino groups onto their surfaces. Rotavirus viral protein 7 (VP7) antibody was attached to the surface of MNBs via these amino groups using a coupling agent, N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP). The antibody-integrated MNBs were incubated with rotavirus-infected cell lysate and then separated from the supernatant by applying a magnetic field. After thorough washing, rotavirus was recovered and enrichment analysis done by polymerase chain reaction (PCR), immunochromatography, and an infection analysis using MA104 cells.Results and discussionImmunochromatography and PCR indicate that anti-rotavirus antibody-integrated MNPs efficiently capture rotavirus with the capsid protein and viral RNA. The estimated recovery rate was 80.2% by PCR and 90.0% by infection analysis, while the concentrating factor was 7.9-fold by PCR and 6.7-fold by infection analysis. In addition, the absence of non-specific binding to the antibody-integrated MNPs was confirmed using anti-dengue virus antibody-integrated MNBs as a negative control.ConclusionThese results suggest that this capture procedure is a useful tool for recovery and enrichment of infectious rotavirus. Moreover, when combined with a suitable virus assay this capture procedure can increase the sensitivity of rotavirus detection. Therefore, this capture method is a valuable tool for generating vaccines as well as for developing sensitive detection systems for viruses.

Ultrasensitive electrochemical detection of microRNA-21 with wide linear dynamic range based on dual signal amplification

Abnormal expression of microRNAs is closely related to human diseases. Ultrasensitive detection of microRNAs with wide linear dynamic range is necessary as the concentrations of microRNAs distributed in biological samples usually range from fM to nM. Here, we constructed an ultrasensitive electrochemical sensor for microRNA-21 based on the integration of a dual signal amplification strategy of hybridization chain reaction (HCR) and enzyme-induced metallization (EIM) with anodic stripping voltammetry (ASV). MicroRNA-21 was captured by capture probe H1 (CP H1) modified magnetic nanobeads (MBs) and amplified by HCR. Multiple alkaline phosphatases (ALP) were coupled based on the specific reaction of biotin and streptavidin. A dual amplification strategy of HCR and EIM enhanced electrochemical signal by approximately 120-fold from the perspectives of target amplification and detection signal amplification, which decreased the detection limit of microRNA-21 to 0.12 fM. Compared to the reports previously reported, a wider linear dynamic range of 2.5 fM to 25 nM spanning 7 orders of magnitude was obtained. The method provides high sensitivity, specificity and a wider linear dynamic range, which shows a great potential in the early diagnosis of diseases.

Selective Capture and Purification of MicroRNAs and Intracellular Proteins through Antisense-vectorized Magnetic Nanobeads

MicroRNAs (miRNAs) are small non-coding nucleotides playing a crucial role in posttranscriptional expression and regulation of target genes in nearly all kinds of cells. In this study, we demonstrate a reliable and efficient capture and purification of miRNAs and intracellular proteins using magnetic nanoparticles functionalized with antisense oligonucleotides. For this purpose, a tumor suppressor miRNA (miR-198), deregulated in several human cancer types, was chosen as the model oligonucleotide. Magnetite nanoparticles carrying the complementary sequence of miR-198 (miR-198 antisense) on their surface were delivered into cells and subsequently used for the extracellular transport of miRNA and proteins. The successful capture of miR-198 was demonstrated by isolating RNA from magnetic nanoparticles followed by real-time PCR quantification. Our experimental data showed that antisense-coated particles captured 5-fold higher amounts of miR-198 when compared to the control nanoparticles. Moreover, several proteins that could play a significant role in miR-198 biogenesis were found attached to miR-198 conjugated nanoparticles and analyzed by mass spectrometry. Our findings demonstrate that a purpose-driven vectorization of magnetic nanobeads with target-specific recognition ligands is highly efficient in selectively transporting miRNA and disease-relevant proteins out of cells and could become a reliable and useful tool for future diagnostic, therapeutic and analytical applications.

An assembly disposable degassing microfluidic device using a gas-permeable hydrophobic membrane and a reusable microsupport array

We introduce an assembly disposable degassing (ADD)-method as a simple and fast active degassing method. The ADD-method is achieved with a microstructured disposable superstrate and a reusable microsupport substrate, which can be assembled and disassembled simply by vacuum pressure. The reusable substrate can be equipped with functionalities to create an elaborately patterned energy field for active manipulation of substances in the microchannel. Degassing performance was evaluated for varying thicknesses of the polydimethylsiloxane (PDMS) membrane and heights of the microsupport array. Based on the ADD-method, an active bubble-trap structure was developed to prevent bubble injection into the microchannels. Deterministic lateral displacement and microvortex devices, as complex structured microfluidic devices that are easily suffered by bubble formation, were used to demonstrate the usefulness of the ADD-method. As a test vehicle of active functional microfluidic devices, an assembly-disposable degassing lateral magnetophoretic microseparator (CTC-addChip) was developed. For the CTC-addChip, a ferromagnetic wire array was inlaid on the reusable substrate to create a high-gradient magnetic field, which can transfer through the PDMS membrane and isolate circulating tumor cells with magnetic nanobeads in the microchannel without bubble interference.

Turn-On Fluorescence Aptasensor on Magnetic Nanobeads for Aflatoxin M1 Detection Based on an Exonuclease III-Assisted Signal Amplification Strategy

In order to satisfy the need for sensitive detection of Aflatoxin M1 (AFM1), we constructed a simple and signal-on fluorescence aptasensor based on an autocatalytic Exonuclease III (Exo III)-assisted signal amplification strategy. In this sensor, the DNA hybridization on magnetic nanobeads could be triggered by the target AFM1, resulting in the release of a single-stranded DNA to induce an Exo III-assisted signal amplification, in which numerous G-quadruplex structures would be produced and then associated with the fluorescent dye to generate significantly amplified fluorescence signals resulting in the increased sensitivity. Under the optimized conditions, this aptasensor was able to detect AFM1 with a practical detection limit of 9.73 ng kg−1 in milk samples. Furthermore, the prepared sensor was successfully used for detection of AFM1 in the commercially available milk samples with the recovery percentages ranging from 80.13% to 108.67%. Also, the sensor performance was evaluated by the commercial immunoassay kit with satisfactory results.

Peptidoglycan binding protein (PGBP)-modified magnetic nanobeads for efficient magnetic capturing of Staphylococcus aureus associated with sepsis in blood

Peptidoglycan-binding protein-modified magnetic nanobeads (PGBP-MNBs) were prepared for efficient magnetic capturing of Staphylococcus aureus (S. aureus), which is associated with sepsis, using the binding affinity of PGBP for the peptidoglycan (PG) layer on S. aureus. These PGBP-MNBs can simply capture S. aureus in plasma within 1 hr or even 15 min. Importantly, they also can capture various types of Gram-positive bacteria, such as Bacillus cereus and methicillin-resistant and methicillin-susceptible S. aureus (MRSA and MSSA). We believe that PGBP-based systems will be used to develop diagnostic systems for Gram-positive bacteria-related diseases.

Engineering a Bacterial Flagella Forest for Sensing and Actuation – A Progress Report

Flagella can be used to make magnetically-controlled microfluidic and nanoscale devices for biomedical applications in both vitro and vivo environments. They are capable of operating with high precision on the cellular and subcellular level. So far, scientists and engineers have successfully used monolithic inorganic materials or photoactive polymers [1] to mimic the helical bacterial flagella whose rotary-propulsion mechanism effectively overcomes the dominant viscous forces that prevail in a low Reynolds-number environment. Here, we focus on bacterial flagella and their rotary motion. The bacterial flagellum is an ideal biomaterial for constructing self-propelling nanoswimmers because it can reversibly change its geometry in response to different environmental stimuli such as pH, the local concentration of certain organic solvents, and mechanical force on the flagella. The bacterial flagellum is very easy to manipulate because it is composed of flagellin which can be mechanically isolated through vortexing and centrifugation, which enables flagella to be used as nanoscale sensors and mechanical transducers. Our project focuses on fabricating a bacterial flagella forest which consists of an ordered array of flagella on a glass substrate. Flagella are attached to magnetic nanobeads via biotin-avidin bonding for actuation by oscillating magnetic field.

Exploring Protein-Inorganic Hybrid Nanoflowers and Immune Magnetic Nanobeads to Detect Salmonella Typhimurium.

Early screening of pathogenic bacteria is key to preventing and controlling outbreaks of foodborne diseases. In this study, protein-inorganic hybrid nanoflowers were synthesized for signal amplification and used with a calcium ion selective electrode (Ca-ISE) to establish a new enzyme-free assay for rapid and sensitive detection of Salmonella. Calcium hydrophosphate crystals were first conjugated with polyclonal antibodies against Salmonella to synthesize immune calcium nanoflowers (CaNFs), and streptavidin modified magnetic nanobeads (MNBs) were conjugated with biotinylated monoclonal antibodies against Salmonella to form immune MNBs. After target bacteria were separated using immune MNBs to form magnetic bacteria, immune CaNFs were conjugated with magnetic bacteria to form nanoflower conjugated bacteria. Then, hydrogen chloride was used to release calcium ions from nanoflower conjugated bacteria. After magnetic separation, the supernatant was finally injected as a continuous-flow to fluidic chip with Ca-ISE for specific detection of calcium ions. The supernatant’s potential had a good linear relationship with bacteria concentration, and this assay was able to detect the S. Typhimurium cells as low as 28 colony forming units/mL within two hours. The mean recovery of target bacteria in spiked chicken samples was 95.0%. This proposed assay shows the potential for rapid, sensitive, and on-line detection of foodborne pathogens.

P-Glycoprotein Detection for Multidrug Resistance of Leukemia Using SERS Immunoassay

Corresponding author: Baoan Chen, MD, PhD; E-mail: cba8888@hotmail.com Zhuyuan Wang, PhD; E-mail: wangzy@seu.edu.cnYiping Cui, PhD; E-mail: cyp@seu.edu.cnKeywords: leukemia; multi-drug resistance; P-glycoprotein; surface-enhanced Raman scattering; SERS intensity.BackgroundAcquisition of multidrug resistance (MDR) in the chemotherapy of leukemia could decrease the survival rate of refractory/relapsing patients. One of the best characterized mechanisms of MDR in leukemia is mediated by multidrug resistance protein-1 and its product, P-glycoprotein (P-gp). Thus, accurate detection of P-gp is necessary for MDR diagnosis. In the recent years, surface-enhanced Raman scattering (SERS) has emerged as a new detection technology of biological label for immunoassay with the advantages of ultrasensitive screening ability and extensive adaptability. However, few researches have focused on the application of SERS immunoassay in the diagnostics of leukemia MDR. The aim of our study is to investigate the expressions of P-gp on the cell surface of K562/ADM cells, and in the whole-blood samples of leukemia using a SERS-based immunoassay technique.MethodsTo simulate the MDR occurrence, we mixed the K562 and K562/ADM cells at different ratios. Besides, we built up the concentration gradient of K562/ADM cells for the quantitative analysis. We also divided 30 blood samples (AML n=14, ALL n=16; female n=12, male n=18; age<60 n=17, age≥60 n=13) into two groups (primary patients in Group A; relapsing patients with over-expressed P-gp in Group B) and compared their SERS-based results with those measured by FCM assay. After preparation of our targeted samples, we synthesized a sandwich immunocomplex, which comprised of magnetic nanobeads (MBs) decorated with anti-CD45, SERS nanoprobes (NPs) decorated with P-gp antibodies, and our targeted samples. Then, SERS measurements were performed on the sandwich immunocomplex. Briefly, the immunocomplex can be precipitated by magnet and the SERS signals could be detected in the precipitates due to the specific binding. Without target samples, only negligible SERS signals could be detected. In this way, the SERS immunoassay can be used to evaluate the presence or expression level of P-gp.ResultsThere were positive and stable SERS signals of peak intensity at 1078 cm-1 after suspended with target samples. First, the SERS intensity of K562/ADM was significantly higher than that of K562 (P <0.01). Second, the SERS intensities of different K562/ADM fractions showed a good linear response to the fractions of K562/ADM cells. Furthermore, the SERS intensities decreased with the decliningK562/ADM concentrations (from 5×106 to 50 cells/mL) and the limit of detection (LOD) could reach 50 cells/ml, which was significantly lower than FCM. Furthermore, the SERS intensity of whole blood samples in Group B were about five folds more than those in Group A (P <0.01). It indicated great application potential and reliability of SERS for MDR assessment in clinic.ConclusionWe have proposed a SERS-based immunoassay to evaluate the expression of P-gp, a product of MDR protein of leukemia. Qualitative and quantitative analysis of K562/ADM indicated excellent specificity, high sensitivity and detection limit, as well as great reproducibility of this immunoassay. It was also demonstrated that this immunoassay was with acceptable accuracy and detection reproducibility for clinical whole blood samples, which was of great importance and convenience for practical clinical application. These features have made SERS-based immunoassay a selective and convenient technique for the identification of leukemia MDR diagnosis. DisclosuresNo relevant conflicts of interest to declare.

Lateral flow immunoassays combining enrichment and colorimetry-fluorescence quantitative detection of sulfamethazine in milk based on trifunctional magnetic nanobeads

In this study, magnetic nanobeads (MNBs) were used as a trifunctional material in lateral flow immunoassay for quantitative detection of sulfamethazine (SM2) in milk. Magnetic enrichment aimed to reduce matrix effects. Naked-eye screening of SM2 was based on colorimetry of colored MNBs. The cut-off value of the naked-eye screening was 25 ng mL−1. When the concentration of SM2 in the samples is equal to the cut-off value or higher, the lateral flow strips can be quantitatively detected via grayscale intensity based on colored MNBs. When the concentration of SM2 in the samples is less than the cut-off value, the lateral flow strips can be quantitatively detected by means of fluorescence intensity based on the fluorescence quenching effect of MNBs. Under optimal conditions, the linear range and limit of detection (LOD) of fluorescence lateral flow immunoassay were 0.033–33 ng mL−1 and 0.026 ng mL−1 respectively, while the linear range and LOD of colorimetric lateral flow immunoassay was 1–100 ng mL−1 and 0.71 ng mL−1, respectively. This novel method can be used for rapid and quantitative detection of SM2 in milk.

Size effects of magnetic beads in circulating tumour cells magnetic capture based on streptavidin-biotin complexation.

Circulating tumour cells (CTCs) draw significant attention as a promising biomarker for cancer prognosis, status monitoring, and metastasis diagnosis. However, the concentration of CTCs in peripheral blood is usually extremely low, thereby requiring enrichment followed by isolation of CTCs prior to detection. An immunomagnetic separation is a promising tool for CTCs enrichment. In this study, a cost-effective magnetic separation method, based on streptavidin-biotin complexation, was developed and the effects of magnetic beads' size in CTCs capture were compared. Magnetic nanobeads which were 25 nm in diameter lead to highest capture efficiency (82.2%) compared with 150 nm magnetic beads and 1 µm microbeads. Based on the streptavidin-biotin system, 25 nm magnetic nanobeads could capture model CTCs over 80% efficiency even at concentrations as low as ∼25 cells/mL that may represent the actual level of CTCs in peripheral blood of cancer patients. Furthermore, the isolated cells remained robust and healthy showing insignificant changes in morphology and behaviour when cultured for 24 h immediately after capture and isolation. The magnetic nanobeads based on streptavidin-biotin complexation showed promise for the easy and efficient capture and isolation of healthy CTCs for further diagnosis and analysis.