Fluorescent-magnetic dual-encoded nanospheres: a promising tool for fast-simultaneous-addressable high-throughput analysis

Multihierarchical Regulation To Achieve Quantum Dot Nanospheres with a Photoluminescence Quantum Yield Close to 100

Quantum dots (QDs) exhibit superior brightness and photochemical stability, making them the preferred option for highly sensitive single-molecule detection compared with fluorescent dyes or proteins. Nevertheless, their high surface energy leads to nonspecific adsorption and poor colloidal stability. In the past decades, we have found that QD-based fluorescent nanoparticles (FNs) can not only address these limitations but also enhance detection sensitivity. However, the photoluminescence quantum yield (PLQY) of FNs is significantly lower compared with that of original QDs. It is urgent to develop a strategy to solve the issue, aiming to further enhance detection sensitivity. In this study, we found that the decrease of PLQY of FNs prepared by free radical polymerization was attributed to two factors: (1) generation of defects that can cause nonradiative transitions resulting from QD-ligands desorption and QD-shell oxidation induced by free radicals; (2) self-absorption resulting from aggregation caused by incompatibility of QDs with polymers. Based on these, we proposed a multihierarchical regulation strategy that includes: (1) regulating QD-ligands; (2) precisely controlling free radical concentration; and (3) constructing cross-linked structures of polymer to improve compatibility and to reduce the formation of surface defects. It is crucial to emphasize that the simultaneous coordination of multiple factors is essential. Consequently, a world-record PLQY of 97.6% for FNs was achieved, breaking through the current bottleneck at 65%. The flexible application of this regulatory concept paves the way for the large-scale production of high-brightness QD-polymer complexes, enhancing their potential applications in sensitive biomedical detection.

Dextran-Functionalized Super-nanoparticle Assemblies of Quantum Dots for Enhanced Cellular Immunolabeling and Imaging

Colloidal semiconductor quantum dots (QDs) are a popular material for applications in bioanalysis and imaging. Although individual QDs are bright, some applications benefit from the use of even brighter materials. One approach to achieve higher brightness is to form super-nanoparticle (super-NP) assemblies of many QDs. Here, we present the preparation, characterization, and utility of dextran-functionalized super-NP assemblies of QDs. Amphiphilic dextran was synthesized and used to encapsulate many hydrophobic QDs via a simple emulsion-based method. The resulting super-NP assemblies or "super-QDs" had hydrodynamic diameters of ca. 90-160 nm, were characterized at the ensemble and single-particle levels, had orders-of-magnitude superior brightness compared to individual QDs, and were non-blinking. Additionally, binary mixtures of red, green, and blue (RGB) colors of QDs were used to prepare super-QDs, including colors difficult to obtain from individual QDs (e.g., magenta). Tetrameric antibody complexes (TACs) enabled simple antibody conjugation for selective cellular immunolabeling and imaging with both an epifluorescence microscope and a smartphone-based platform. The technical limitations of the latter platform were overcome by the increased per-particle brightness of the super-QDs, and the super-QDs outperformed individual QDs in both cases. Overall, the super-QDs are a very promising material for bioanalysis and imaging applications where brightness is paramount.

Optically Sensitive and Magnetically Identifiable Supraparticles as Indicators of Surface Abrasion

Identifying and ensuring the integrity of products plays an important role in today's globalized world. Miniaturized information taggants in the packaging surface are therefore required to monitor the product itself instead of applying external labels. Ideally, multiple types of information are stored in such additives. In this work, micrometer-sized core-shell particles (supraparticles) were developed to provide material surfaces with both an identifier and a surface abrasion indication functionality. The core of the supraparticles contains iron oxide nanoparticles that allow identification of the surface with a spectral magnetic code resolved by magnetic particle spectroscopy. The fluorescent silica nanoparticles in the supraparticle shell can be abraded by mechanical stress and resolved by fluorescence spectroscopy. This provides information about the mechanical integrity of the system. The application as surfaces, that contain several types of information in one supraparticle, was demonstrated here by incorporating such bifunctional supraparticles as additives in a surface coating.

Colorful Luminescent Magnetic Supraparticles: Expanding the Applicability, Information Capacity, and Security of Micrometer-Scaled Identification Taggants by Dual-Spectral Encoding

(Sub)micrometer-scaled identification (ID) taggants enable direct identification of arbitrary goods, thereby opening up application fields based on the possibility of tracking, tracing, and anti-counterfeiting. Due to their small dimensions, these taggants can equip in principle even the smallest subcomponents or raw materials with information. To achieve the demanded applicability, the mostly used optically encoded ID taggants must be further improved. Here, micrometer-scaled supraparticles with spectrally encoded luminescent and magnetically encoded signal characteristics are reported. They are produced in a readily customizable bottom-up fabrication procedure that enables precise adjustment of luminescent and magnetic properties on multiple hierarchy levels. The incorporation of commonly used magnetic nanoparticles and fluorescent dyes, respectively, into polymer nanocomposite particles, establishes a convenient toolbox of magnetic and luminescent building blocks. The subsequent assembly of selected building blocks in the desired ratios into supraparticles grants for all the flexibility to freely adjust both signal characteristics. The obtained spectrally resolved visible luminescent and invisible magnetic ID signatures are complementary in nature, thus expanding applicability and information security compared to recently reported optical- or magnetic-encoded taggants. Additionally, the introduced ID taggant supraparticles can significantly enhance the coding capacity. Therefore, the introduced supraparticles are considered as next-generation ID taggants.

Tailor made magnetic nanolights: fabrication to cancer theranostics applications

Nanoparticles having magnetic and fluorescent properties could be considered as a gift to materials scientists due to their unique magneto-optical qualities. Multiple component particles can overcome challenges related with a single component and unveil bifunctional/multifunctional features that can enlarge their applications in diagnostic imaging agents and therapeutic delivery vehicles. Bifunctional nanoparticles that have both luminescent and magnetic features are termed as magnetic nanolights. Herein, we present recent progress of magneto-fluorescent nanoparticles (quantum dots based magnetic nanoparticles, Janus particles, and heterocrystalline fluorescent magnetic materials), comprehensively describing fabrication strategies, types, and biomedical applications. In this review, our aim is not only to encompass the preparation strategies of these special types of magneto-fluorescent nanomaterials but also their extensive applications in bioimaging techniques, cancer therapy (targeted and hyperthermic), and sustained release of active agents (drugs, proteins, antibodies, hormones, enzymes, growth factors).

Precisely Encoded Barcodes through the Structure-Fluorescence Combinational Strategy: A Flexible, Robust, and Versatile Multiplexed Biodetection Platform with Ultrahigh Encoding Capacities

With the rapid development of suspension array technology, microbeads-based barcodes as the core element with sufficient encoding capacity are urgently required for high-throughput multiplexed detection. Here, a novel structure-fluorescence combinational encoding strategy is proposed for the first time to establish a barcode library with ultrahigh encoding capacities. Based on the never revealed transformability of the structural parameters (e.g., porosity and matrix component) of mesoporous microbeads into scattering signals in flow cytometry, the enlargement of codes number has been successfully realized in combination with two other fluorescent elements of fluorescein isothiocyanate isomer I (FITC) and quantum dots (QDs). The barcodes are constructed with precise architectures including FITC encapsulated within mesopores and magnetic nanoparticles as well as QDs immobilized on the outer surface to achieve the ultrahigh encoding level of 300 accompanied with superparamagnetism. To the best of knowledge, it is the highest record of single excitation laser-based encoding capacity up to now. Moreover, a ten-plexed tumor markers bioassay based on the tailored-designed barcodes has been evaluated to confirm their feasibility and effectiveness, and the results indicate that the barcodes platform is a promising and robust tool for practical multiplexed biodetection.

The Role of Suspension Array Technology in Rapid Detection of Foodborne Pollutants: Applications and Future Challenges

Food safety is an important livelihood issue, which has always been focused attention by countries and governments all over the world. As food supply chains are becoming global, food quality control is essential for consumer protection as well as for the food industry. In recent years, a great part of food analysis is carried out using new techniques for rapid detection. As the first biochip technology that has been approved by the Food and Drug Administration (FDA), there is an increasing interest in suspension array technology (SAT) for food and environmental analysis with advantages of rapidity, high accuracy, sensitivity, and throughput. Therefore, it is important for researchers to understand the development and application of this technology in food industry. Herein, we summarized the principle and composition of SAT and its application in food safety monitoring. The utility of SAT in detection of foodborne microorganisms, residues of agricultural and veterinary drugs, genetically modified food and allergens in recent years is elaborated, and the further development direction of SAT is envisaged.

Rapid screening and quantitative detection of Salmonella using a quantum dot nanobead-based biosensor

A quantum dot nanobead-based sensor is demonstrated for Salmonella detection with balanced sensitivity, specificity and high accuracy.

Fluorescent-Magnetic-Catalytic Nanospheres for Dual-Modality Detection of H9N2 Avian Influenza Virus

The outbreak of H9N2 avian influenza virus (H9N2 AIV) brings high mortality and huge economic losses every year. Sensitive and reliable detection methods are essential to timely diagnosis and treatment. Herein, a dual-modality immunoassay is proposed for H9N2 AIV detection by employing fluorescent-magnetic-catalytic nanospheres (FMCNs) as labels and alkaline phosphatase (ALP)-induced metallization as a signal amplification strategy. The excellent magnetic properties of FMCNs endow the assay a potential application in complex samples. Also, the excellent fluorescence properties of FMCNs enable fluorescence modality readout. The antibodies on the FMCN surface can achieve efficient capture and separation of targets. Amplified electrochemical modality readout can be obtained through ALP-catalyzed silver deposition. Dual-modality immunoassay combined the advantages of electrochemical assay with fluorescence assay and provides accurate detection results to meet different testing needs. With two quantitative analysis forms, H9N2 AIV can be detected by electrochemical signals with a quantitation range of 0.1 to 1000 ng/mL and a detection limit of 10 pg/mL. The linear range is 300 to 1000 ng/mL with a detection limit of 69.8 ng/mL by the fluorescence signal readout. Moreover, the specificity, anti-interference ability, accuracy, and diversity of the proposal have unlimited potential for early diagnosis of suspect infections.

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.

Preparation of Fluorescence-Encoded Microspheres Based on Hydrophobic Conjugated Polymer-Dye Combination and the Immunoassay

Fluorescent microspheres are greatly demanded in many applications based on high-throughput suspension array technology. To realize the multiplexed assay, microspheres should be encoded to identify the interaction between analytes and spheres. This study advanced a strategy for preparing fluorescence-encoded microspheres, employing two hydrophobic fluorophores, poly(p-phenyleneethylene) (PPE), and Nile Red (NR), as well as the monodisperse amino-modified porous substrate polymeric spheres, poly(glycidyl methacrylate) microspheres (APGMA). Loading the fluorophores sequentially onto the substrate spheres via adsorption by immersing the spheres in the dipping solution of fluorophores resulted in the APGMA-PPE-NR spheres. By varying the concentration and combination of fluorophores in the solution, an array of 64-code APGMA-PPE-NR spheres was obtained and could be easily individually decoded via flow cytometry. A 2D dot plot from the flow cytometry of a set of mixed spheres with four different codes could also be differentiated, coincident with the overlaid plots of the spheres' corresponding codes but measured individually. These spheres were found to have good stability against washing, photobleaching, and thermal treatment. In addition, a sandwich immunoassay for the detection of goat IgG was performed, and the capability of the encoded spheres to be used in suspension array technology was demonstrated.

Fluorescent microbeads for point-of-care testing: a review

Microbead-based point-of-care testing (POCT) has demonstrated great promise in translating detection modalities from bench-side to bed-side. This is due to the ease of visualization, high surface area-to-volume ratio of beads for efficient target binding, and efficient encoding capability for simultaneous detection of multiple analytes. This review (with 112 references) summarizes the progress made in the field of fluorescent microbead-based POCT. Following an introduction into the field, a first large section sums up techniques and materials for preparing microbeads, typically of dye-labelled particles, various kinds of quantum dots and upconversion materials. Further subsections cover the encapsulation of nanoparticles into microbeads, decoration of nanoparticles on microbeads, and in situ embedding of nanoparticles during microbead synthesis. A next large section summarizes microbead-based fluorometric POCT, with subsections on detection of nucleic acids, proteins, circulating tumor cells and bacteria. A further section covers emerging POCT based on the use of smartphones or flexible microchips. The last section gives conclusions and an outlook on current challenges and possible solutions. Aside from giving an overview on the state of the art, we expect this article to boost the further development of POCT technology. Graphical Abstract Schematic presentation of the fabrication of microbeads, the detection targets of interest including bacteria, circulating tumor cells (CTCs), protein and nucleic acid, and the emerging point-of-care testing (POCT) platform. The colored wheels of the bus represent the fluorescent materials embedded in (red color) or decorated on the surface of microbeads (green color).

Colorimetric-Fluorescent-Magnetic Nanosphere-Based Multimodal Assay Platform for Salmonella Detection

Rapid and sensitive foodborne pathogen detection assay, which can be applied in multiple fields, is essential to timely diagnosis. Herein, we proposed a multisignal readout lateral flow immunoassay for Salmonella typhimurium ( S. typhi) detection. The assay employs colorimetric-fluorescent-magnetic nanospheres (CFMNs) as labels, which possess multifunctional target separation and enrichment, multisignal readout, and two formats of quantitation. The assay for S. typhi detection involves magnetic separation and chromatography. First, the S. typhi were separated and enriched from matrix by antibody labeled CFMNs, and then the S. typhi-containing suspension is added onto the sample pad to flow up the test strip. The introduction of magnetic separation enhances anti-interference ability and 10-fold sensitivity, making the assay possible for practical application. The assay has realized naked eye detection of 1.88 × 10⁴ CFU/mL S. typhi, and 3.75 × 10³ CFU/mL S. typhi can be detected with a magnetic assay reader, which is 2-4 orders of magnitude lower than other label-based LFIAs, with a quantitation range of 1.88 × 10⁴ to 1.88 × 10⁷ CFU/mL by measuring the fluorescence intensity and magnetic signal. Moreover, the successful detection of S. typhi in complex matrix (tap water, milk, fetal bovine serum, and whole blood) indicated its potential application in real samples.

Sensitive detection of Campylobacter jejuni using one-step strategy based on functional nanospheres of immunomagnetic capture and quantum dots

Campylobacter jejuni has emerged as the most common bacterial foodborne illness in the developed world. Here, we demonstrate a convenient one-step strategy for detecting C. jejuni. Immunomagnetic nanospheres (IMNS) and immunofluorescent nanospheres (IFNS, quantum dots) were used for the simultaneous, sensitive capture and recognition of C. jejuni. After magnetic separation with the IMNS, detection of C. jejuni was achieved with fluorescence measurement of the IFNS in the sandwich complexes (IMNS-bacteria-IFNS). The limit of detection of this assay was 10³ CFU/mL, and the linear range was from 10⁵ to 10⁷ CFU/mL (R² = 0.9994). When compared with a conventional two-step detection strategy, in which C. jejuni was first captured with the IMNS and then detected using the IFNS, this one-step detection strategy enhance sensitivity and save time. This suggested that the developed method has the potential for use as an alternative to the standard method for food quality assurance, as it provides rapid detection of C. jejuni in foodstuffs and the environment.

Polymers mediate a one-pot route for functionalized quantum dot barcodes with a large encoding capacity

With the increasing demands for high-throughput multiplexed bioassays, quantum dot (QD)-encoded microbeads as biocarriers for various bioreactions have attracted considerable attention. However, three key requirements for these biocarriers are still longstanding issues: a stable fluorescence intensity, a large encoding capacity and abundant surface functional groups. Here, a novel one-pot strategy is developed, generating functionalized QD-encoded microspheres with a strong fluorescence intensity and optical stability. With poly(styrene-co-maleic anhydride) (PSMA) molecules as mediators, the encapsulation of QDs and carboxylation of the bead surface are integrated together, greatly improving the preparation efficiency and guaranteeing their potential application in biodetection. Moreover, the mechanism for preparing QD-doped beads is further proposed, which helps to precisely manipulate the preparation process and accurately encode the beads. Through this approach, a single- and dual-color barcode library of QD-encoded microspheres has been successfully established, which demonstrates their great potential in suspension arrays.

Recent Progress in Synthesis and Functionalization of Multimodal Fluorescent-Magnetic Nanoparticles for Biological Applications

There is a great interest in the development of new nanomaterials for multimodal imaging applications in biology and medicine. Multimodal fluorescent-magnetic based nanomaterials deserve particular attention as they can be used as diagnostic and drug delivery tools, which could facilitate the diagnosis and treatment of cancer and many other diseases. This review focuses on the recent developments of magnetic-fluorescent nanocomposites and their biomedical applications. The recent advances in synthetic strategies and approaches for the preparation of fluorescent-magnetic nanocomposites are presented. The main biomedical uses of multimodal fluorescent-magnetic nanomaterials, including biological imaging, cancer therapy and drug delivery, are discussed, and prospects of this field are outlined.

Efficient Enrichment and Analyses of Bacteria at Ultralow Concentration with Quick-Response Magnetic Nanospheres

Enrichment and purification of bacteria from complex matrices are crucial for their detection and investigation, in which magnetic separation techniques have recently show great application advantages. However, currently used magnetic particles all have their own limitations: Magnetic microparticles exhibit poor binding capacity with targets, while magnetic nanoparticles suffer slow magnetic response and high loss rate during treatment process. Herein, we used a highly controllable layer-by-layer assembly method to fabricate quick-response magnetic nanospheres (MNs), and with Salmonella typhimurium as a model, we successfully achieve their rapid and efficient enrichment. The MNs combined the advantages of magnetic microparticles and nanoparticles. On the one hand, the MNs had a fast magnetic response, and almost 100% of the MNs could be recovered by 1 min attraction with a simple magnetic scaffold. Hence, using antibody conjugated MNs (immunomagnetic nanospheres, IMNs) to capture bacteria hardly generated loss and did not need complex separation tools or techniques. On the other hand, the IMNs showed much excellent capture capacity. With 20 min interaction, almost all of the target bacteria could be captured, and even only one bacterium existing in the samples was not missed, comparing with the immunomagnetic microparticles which could only capture less than 50% of the bacteria. Besides, the IMNs could achieve the same efficient enrichment in complex matrices, such as milk, fetal bovine serum, and urine, demonstrating their good stability, strong anti-interference ability, and low nonspecific adsorption. In addition, the isolated bacteria could be directly used for culture, polymerase chain reaction (PCR) analyses, and fluorescence immunoassay without a release process, which suggested our IMNs-based enrichment strategy could be conveniently coupled with the downstream identification and analysis techniques. Thus, the MNs provided by this work showed great superiority in bacteria enrichment, which would be a promising tool for bacteria detection and investigation.

Fluorescent/magnetic micro/nano-spheres based on quantum dots and/or magnetic nanoparticles: preparation, properties, and their applications in cancer studies

The study of cancer is of great significance to human survival and development, due to the fact that cancer has become one of the greatest threats to human health. In recent years, the rapid progress of nanoscience and nanotechnology has brought new and bright opportunities to this field. In particular, the applications of quantum dots (QDs) and magnetic nanoparticles (MNPs) have greatly promoted early diagnosis and effective therapy of cancer. In this review, we focus on fluorescent/magnetic micro/nano-spheres based on QDs and/or MNPs (we may call them "nanoparticle-sphere (NP-sphere) composites") from their preparation to their bio-application in cancer research. Firstly, we outline and compare the main four kinds of methods for fabricating NP-sphere composites, including their design principles, operation processes, and characteristics (merits and limitations). The NP-sphere composites successfully inherit the unique fluorescence or magnetic properties of QDs or MNPs. Moreover, compared with the nanoparticles (NPs) alone, the NP-sphere composites show superior properties, which are also discussed in this review. Then, we summarize their recent applications in cancer research from three aspects, that is: separation and enrichment of target tumor cells or biomarkers; cancer diagnosis mainly through medical imaging or tumor biomarker detection; and cancer therapy via targeted drug delivery systems. Finally, we provide some perspectives on the future challenges and development trends of the NP-sphere composites.

A chip assisted immunomagnetic separation system for the efficient capture and in situ identification of circulating tumor cells

The detection of circulating tumor cells (CTCs), a kind of "liquid biopsy", represents a potential alternative to noninvasive detection, characterization and monitoring of carcinoma. Many previous studies have shown that the number of CTCs has a significant relationship with the stage of cancer. However, CTC enrichment and detection remain notoriously difficult because they are extremely rare in the bloodstream. Herein, aided by a microfluidic device, an immunomagnetic separation system was applied to efficiently capture and in situ identify circulating tumor cells. Magnetic nanospheres (MNs) were modified with an anti-epithelial-cell-adhesion-molecule (anti-EpCAM) antibody to fabricate immunomagnetic nanospheres (IMNs). IMNs were then loaded into the magnetic field controllable microfluidic chip to form uniform IMN patterns. The IMN patterns maintained good stability during the whole processes including enrichment, washing and identification. Apart from its simple manufacture process, the obtained microfluidic device was capable of capturing CTCs from the bloodstream with an efficiency higher than 94%. The captured cells could be directly visualized with an inverted fluorescence microscope in situ by immunocytochemistry (ICC) identification, which decreased cell loss effectively. Besides that, the CTCs could be recovered completely just by PBS washing after removal of the permanent magnets. It was observed that all the processes showed negligible influence on cell viability (viability up to 93%) and that the captured cells could be re-cultured for more than 5 passages after release without disassociating IMNs. In addition, the device was applied to clinical samples and almost all the samples from patients showed positive results, which suggests it could serve as a valuable tool for CTC enrichment and detection in the clinic.

Rapid and Quantitative Detection of Avian Influenza A(H7N9) Virions in Complex Matrices Based on Combined Magnetic Capture and Quantum Dot Labeling

Avian influenza A(H7N9) virus, which emerged in China in the spring of 2013, has infected hundreds of people and resulted in many deaths. Herein, a rapid and quantitative assay is proposed for the one-step detection of H7N9 virions. Immunomagnetic nanospheres (IMNs) and antibody-conjugated quantum dots (Ab-QDs) are simultaneously employed to capture and identify the target virus, leading to a high efficiency, good specificity, and strong anti-interference ability. Moreover, this reliable detection assay, which combines the efficient magnetic enrichment and the unique photophysical properties of QDs, can achieve a high sensitivity for a low detection limit. At the same time, this detection strategy shows great flexibility for employment in a variety of fluorescence detectors, including fluorescence spectrometry, microscope assays, and handheld UV lamp tests. Furthermore, our one-step detection strategy induces very little change in the integrity of the vulnerable virions, which enables additional genotyping testing following the fluorescence detection. The present study, thus, reports a rapid and quantitative approach for the detection of H7N9 virions based on simultaneous magnetic capture and QD labeling, thereby providing a higher probability for detection and therefore faster diagnosis of H7N9-infected patients.

Combination of dynamic magnetophoretic separation and stationary magnetic trap for highly sensitive and selective detection of Salmonella typhimurium in complex matrix

Foodborne illnesses have always been a serious problem that threats public health, so it is necessary to develop a method that can detect the pathogens rapidly and sensitively. In this study, we designed a magnetic controlled microfluidic device which integrated the dynamic magnetophoretic separation and stationary magnetic trap together for sensitive and selective detection of Salmonella typhimurium (S. typhimurium). Coupled with immunomagnetic nanospheres (IMNs), this device could separate and enrich the target pathogens and realize the sensitive detection of target pathogens on chip. Based on the principle of sandwich immunoassays, the trapped target pathogens identified by streptavidin modified QDs (SA-QDs) were detected under an inverted fluorescence microscopy. A linear range was exhibited at the concentration from 1.0×10(4) to 1.0×10(6) colony-forming units/mL (CFU/mL), the limit of detection (LOD) was as low as 5.4×10(3) CFU/mL in milk (considering the sample volume, the absolute detection limit corresponded to 540C FU). Compared with the device with stationary magnetic trap alone, the integrated device enhanced anti-interference ability and increased detection sensitivity through dynamic magnetophoretic separation, and made the detection in complex samples more accurate. In addition, it had excellent specificity and good reproducibility. The developed system provides a rapid, sensitive and accurate approach to detect pathogens in practice samples.

Quick-response magnetic nanospheres for rapid, efficient capture and sensitive detection of circulating tumor cells

The study on circulating tumor cells (CTCs) has great significance for cancer prognosis, treatment monitoring, and metastasis diagnosis, in which isolation and enrichment of CTCs are key steps due to their extremely low concentration in peripheral blood. Herein, magnetic nanospheres (MNs) were fabricated by a convenient and highly controllable layer-by-layer assembly method. The MNs were nanosized with fast magnetic response, and nearly all of the MNs could be captured by 1 min attraction with a commercial magnetic scaffold. In addition, the MNs were very stable without aggregation or precipitation in whole blood and could be re-collected nearly at 100% in a monodisperse state. Modified with anti-epithelial-cell-adhesion-molecule (EpCAM) antibody, the obtained immunomagnetic nanospheres (IMNs) successfully captured extremely rare tumor cells in whole blood with an efficiency of more than 94% via only a 5 min incubation. Moreover, the isolated cells remained viable at 90.5 ± 1.2%, and they could be directly used for culture, reverse transcription-polymerase chain reaction (RT-PCR), and immunocytochemistry (ICC) identification. ICC identification and enumeration of the tumor cells in the same blood samples showed high sensitivity and good reproducibility. Furthermore, the IMNs were successfully applied to the isolation and detection of CTCs in cancer patient peripheral blood samples, and even one CTC in the whole blood sample was able to be detected, which suggested they would be a promising tool for CTC enrichment and detection.

Optically encoded multifunctional nanospheres for one-pot separation and detection of multiplex DNA sequences

In this study, we report a simple method for simultaneous detection of multiplex DNA sequences, including complementary DNA (cDNA) sequences of HIV and HCV, DNA sequence of HBV, with QDs-encoded fluorescent nanospheres and nano-γ-Fe2O3-coated magnetic nanospheres. Detection was achieved on a fluorescence spectrophotometer without additional auxiliary instruments, and the detection limit was about 100 pM. Here, QDs-encoded fluorescent nanospheres (FNS) with different photoluminescent properties, and magnetic nanospheres (MNS) were separately fabricated by stepwise assembly of hydrophobic QDs or nano-γ-Fe2O3 on the surface of branched poly(ethylene imine) (PEI)-coated nanospheres in precisely controlled amounts, finally followed by silica encapsulation. FNS-labeled probe DNAs and MNS-labeled capture DNAs were used to hybridize with the corresponding targets at the same time. After magnetic separation, the sandwich-structured adducts were measured by fluorescence spectrophotometry. The results indicated that the targets could be detected with high sensitivity. This method is convenient, fast enough, and capable of high anti-interference. Therefore, it is expected to be used for simultaneous detection and separation of multiple targets at high levels of purity and throughput.