Bioinspired Photonic Barcodes with Graphene Oxide Encapsulation for Multiplexed MicroRNA Quantification

Hydrogel-Encased Photonic Microspheres with Enhanced Color Saturation and High Suspension Stability

Regular arrays of colloidal particles can produce striking structural colors without the need for any chemical pigments. Regular arrays of colloidal particles can be processed into microparticles via emulsion templates for use as structural colorants. Photonic microparticles, however, suffer from intense incoherent scattering and lack of suspension stability. We propose a microfluidic technique to generate hydrogel-shelled photonic microspheres that display enhanced color saturation and suspension stability. We created these microspheres using oil-in-water-in-oil (O/W/O) double-emulsion droplets with well-defined dimensions with a capillary microfluidic device. The inner oil droplet contains silica particles in a photocurable monomer, while the middle water droplet carries the hydrogel precursor. Within the inner oil droplet, silica particles arrange into crystalline arrays due to solvation-layer-induced interparticle repulsion. UV irradiation solidifies the inner photonic core and the outer hydrogel shell. The hydrogel shell reduces white scattering and enhances the suspension stability in water. Notably, the hydrogel precursor in the water droplet aids in maintaining the solvation layer, resulting in enhanced crystallinity and richer colors compared with microspheres from O/W single-emulsion droplets. These hydrogel-encased photonic microspheres show promise as structural colorants in water-based inks and polymer composites.

A true color palette: binary metastable photonic pigments

Different from the traditional concept that binary photonic crystals can only reproduce mixed colors due to the simple superposition of the photonic band gaps, precisely addressable "true colors" obtained from volume fraction deviation of binary photonic crystals with metastable structures are reported here. Inspired by the mussels' adhesion and longhorn beetles' photonic scales, a binary metastable amorphous photonic crystal was obtained by enhancing the driving forces and customizing the surface roughness of building blocks to regulate the thermodynamic and dynamic factors simultaneously. By controlling the volume fraction of two building blocks, the tunable photonic bandgap varies linearly in the visible region. Furthermore, the "true violet" that cannot be obtained by conventional color mixing is reproduced with the particular ultraviolet characteristics of red photonic pigment's metastable structures, which complement the palette effect of "true colors". Meanwhile, due to the self-adhesion and post-modification of building blocks, the stability of photonic pigments is further improved. The binary photonic pigments not only solve the dilemma of mixed colors, but also realize the tunability and multiplicity of "true colors", offering a new choice for the color palette of the world.

Bioinspired Perovskite Nanocrystals-Integrated Photonic Crystal Microsphere Arrays for Information Security

Information security occupies an important position in the era of big data. Attempts to improve the security performance tend to impart them with more additional encryption strategies. Herein, inspired by the wettability feature of Stenocara beetle elytra and signal model of traffic light, a novel array of perovskite nanocrystals (PNs)-integrated PhC microsphere for information security is presented. The photoluminescent PNs are encapsulated in angle-independent PhC microspheres to impart them with binary optical signals as coding information. Through the multimask superposition approach, PNs-integrated PhC microspheres with different codes are placed into fluorosilane-treated PDMS substrate to form different arrays. These arrays could converge moisture on PhC microspheres in wet environment, which avoids the ions loss of the PNs and effectively prevented mutual contamination. In addition, the fluorescence of the PNs inside PhC microspheres could reversibly quench or recover in response to the environmental moisture. Based on these features, it is demonstrated that the PNs-integrated PhC microsphere arrays could realize various information encryption modes, which indicate their excellent values in information security fields.

An array-based nanosensor for detecting cellular responses in macrophages induced by femtomolar levels of pesticides

Environmental agents can induce cellular responses at concentrations far below the limits of detection for current viability and biomarker-based cell sensing platforms. Hypothesis-free cell sensor platforms can be engineered to maximize sensitivity to phenotypic changes, providing a tool for lowering the threshold for detecting cellular changes. Pesticides are one of the most prevalent sources of chemical exposure due to their use in food and agriculture fields. We report here a FRET-based nanosensor array engineered to maximize responses to changes at cell surfaces after pesticide exposure. This sensor array robustly detected macrophage responses to femtomolar concentrations of common pesticides-orders of magnitude lower concentrations than traditional toxicological and biomarker-based strategies. Significantly, this platform was able to classify these responses by pesticide class, demonstrating the ability to distinguish between changes induced by these different agents. Taken together, hypothesis-free cell surface sensing is a promising tool for detecting the effects of ultra-trace environmental chemicals on human health, as well as detecting threshold responses for use in drug discovery and diagnostics.

Single cell multi-miRNAs quantification with hydrogel microbeads for liver cancer cell subtypes discrimination

The simultaneous quantification of multi-miRNAs in single cells reveals cellular heterogeneity, and benefits the subtypes discrimination of cancer cells . Though micro-droplet techniques enable successful single cell encapsulation, the isolated and restricted reaction space of microdroplets causes cross-reactions and inaccuracy for simultaneous multi-miRNAs quantification. Herein, we develop a hydrogel microbead based strategy for the simultaneous sensitive quantification of miRNA-21, 122 and 222 in single cells. Single cells are encapsulated and undergo cytolysis in hydrogel microbeads. The three target miRNAs are retained in the microbead by pre-immobilized capture probes, and activate rolling circle amplification (RCA) reactions. The RCA products are hybridized with corresponding dye labelled DNA reporters, and the respective fluorescence intensities are recorded for multi-miRNA quantification. The porous structure of the hydrogel microbeads allows the free diffusion of reactants and easy removal of unreacted DNA strands, which effectively avoids nonspecific cross-reactions. Clear differentiation of cellular heterogeneity and subpopulation discrimination are achieved for three kinds of liver cancer cells and one normal liver cell.

A single cell multi-miRNAs quantification strategy is reported. Single cells are encapsulated and undergo cytolysis in hydrogel microbeads, then the quantitative analysis of three miRNAs is used to achieve sub-populations discrimination for liver cells.

From Passive Signal Output to Intelligent Response: "On-Demand" Precise Imaging Controlled by Near-Infrared Light

"On-demand" accurate imaging of multiple intracellular miRNAs will significantly improve the detection reliability and accuracy. However, the "always-active" design of traditional multicomponent detection probes enables them to passively recognize and output signals as soon as they encounter targets, which will inevitably impair the detection accuracy and, inevitably, result in false-positive signals. To address this scientific problem, in this work, we developed a near-infrared (NIR) light-activated multicomponent detection intelligent nanoprobe for spatially and temporally controlled on-demand accurate imaging of multiple intracellular miRNAs. The proposed intelligent nanoprobe is composed of a rationally designed UV light-responsive triangular DNA nano sucker (TDS) and upconversion nanoparticles (UCNPs), named UCNPs@TDS (UTDS), which can enter cells autonomously through endocytosis and enable remote regulation of on-demand accurate imaging for multiple intracellular miRNAs using NIR light illumination at a chosen time and place. It is worth noting that the most important highlight of the UTDS we designed in this work is that it can resist nonspecific activation as well as effectively avoid false-positive signals and improve the accuracy of imaging of multiple intracellular miRNAs. Moreover, distinguishing different kinds of cell lines with different miRNA expressions levels can be also achieved through this NIR light-activated intelligent UTDS, showing feasible prospects in precise imaging and disease diagnosis.

Bottom-Up Assembled Photonic Crystals for Structure-Enabled Label-Free Sensing

Photonic crystals (PhCs) display photonic stop bands (PSBs) and at the edges of these PSBs transport light with reduced velocity, enabling the PhCs to confine and manipulate incident light with enhanced light-matter interaction. Intense research has been devoted to leveraging the optical properties of PhCs for the development of optical sensors for bioassays, diagnosis, and environmental monitoring. These applications have furthermore benefited from the inherently large surface area of PhCs, giving rise to high analyte adsorption and the wide range of options for structural variations of the PhCs leading to enhanced light-matter interaction. Here, we focus on bottom-up assembled PhCs and review the significant advances that have been made in their use as label-free sensors. We describe their potential for point-of-care devices and in the review include their structural design, constituent materials, fabrication strategy, and sensing working principles. We thereby classify them according to five sensing principles: sensing of refractive index variations, sensing by lattice spacing variations, enhanced fluorescence spectroscopy, surface-enhanced Raman spectroscopy, and configuration transitions.

From colloidal particles to photonic crystals: advances in self-assembly and their emerging applications

Over the last three decades, photonic crystals (PhCs) have attracted intense interests thanks to their broad potential applications in optics and photonics. Generally, these structures can be fabricated via either "top-down" lithographic or "bottom-up" self-assembly approaches. The self-assembly approaches have attracted particular attention due to their low cost, simple fabrication processes, relative convenience of scaling up, and the ease of creating complex structures with nanometer precision. The self-assembled colloidal crystals (CCs), which are good candidates for PhCs, have offered unprecedented opportunities for photonics, optics, optoelectronics, sensing, energy harvesting, environmental remediation, pigments, and many other applications. The creation of high-quality CCs and their mass fabrication over large areas are the critical limiting factors for real-world applications. This paper reviews the state-of-the-art techniques in the self-assembly of colloidal particles for the fabrication of large-area high-quality CCs and CCs with unique symmetries. The first part of this review summarizes the types of defects commonly encountered in the fabrication process and their effects on the optical properties of the resultant CCs. Next, the mechanisms of the formation of cracks/defects are discussed, and a range of versatile fabrication methods to create large-area crack/defect-free two-dimensional and three-dimensional CCs are described. Meanwhile, we also shed light on both the advantages and limitations of these advanced approaches developed to fabricate high-quality CCs. The self-assembly routes and achievements in the fabrication of CCs with the ability to open a complete photonic bandgap, such as cubic diamond and pyrochlore structure CCs, are discussed as well. Then emerging applications of large-area high-quality CCs and unique photonic structures enabled by the advanced self-assembly methods are illustrated. At the end of this review, we outlook the future approaches in the fabrication of perfect CCs and highlight their novel real-world applications.

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.

Advances in multiplexed techniques for the detection and quantification of microRNAs

MicroRNA detection is currently a crucial analytical chemistry challenge: almost 2000 papers were referenced in PubMed in 2018 and 2019 for the keywords "miRNA detection method". MicroRNAs are potential biomarkers for multiple diseases including cancers, neurodegenerative and cardiovascular diseases. Since miRNAs are stably released in bodily fluids, they are of prime interest for the development of non-invasive diagnosis methods, such as liquid biopsies. Their detection is however challenging, as high levels of sensitivity, specificity and robustness are required. The analysis also needs to be quantitative, since the aim is to detect miRNA concentration changes. Moreover, a high multiplexing capability is also of crucial importance, since the clinical potential of miRNAs probably lays in our ability to perform parallel mapping of multiple miRNA concentrations and recognize typical disease signature from this profile. A plethora of biochemical innovative detection methods have been reported recently and some of them provide new solutions to the problem of sensitive multiplex detection. In this review, we propose to analyze in particular the new developments in multiplexed approaches to miRNA detection. The main aspects of these methods (including sensitivity and specificity) will be analyzed, with a particular focus on the demonstrated multiplexing capability and potential of each of these methods.

Catalytic Hairpin Self-Assembly-Based SERS Sensor Array for the Simultaneous Measurement of Multiple Cancer-Associated miRNAs

The abnormal expression of some miRNAs is often closely related to the development of tumors. Available detection methods or biosensors that can simultaneously quantify multiple miRNAs in a single sample have rarely been reported. Herein, a novel catalytic hairpin self-assembly (CHA)-based surface-enhanced Raman scattering (SERS) sensor array was developed to simultaneously measure multiple miRNAs associated with cancer in one sample. The sensor array with four different sensing units was constructed by immobilizing one of four different hairpin-structured DNA sequence 1 (hp1) onto one of four Au/Ag alloy nanoparticle (AuAgNP)-coated detection wells. When target miRNA is present, the SERS tags, which were prepared by modifying AuAgNPs with a Raman reporter molecule of 4-mercaptobenzonitrile (MPBN) and the related hairpin-structured DNA sequence 2 (hp2), were captured onto the corresponding sensor unit through a repeated specific CHA reaction. This generated many "hot spots" because of interactions between the SERS tags and the AuAgNP layer-coated surface of the sensor, which ultimately produced a strong SERS signal that allowed the detection of target miRNAs with the detection limit of 0.15 pM. Using this SERS sensor array, multiple cancer-associated miRNAs (miR-1246, miR-221, miR-133a, and miR-21) were successfully determined in buffer, serum, and cellular RNA extracts.

Bioinspired structural color particles with multi-layer graphene oxide encapsulated nanoparticle components

Because of the unique features of spherical symmetry, angle-independency, good monodispersity, controllable components and morphologies, structural color particles (SCPs) have found great significances in various fields such as sensing, monitoring, biological assays, etc. Here, inspired by the melanosome-derived bright structural colors and the self-adhesivity of mussels, we present a kind of bioinspired SCPs assembled from polydopamine (PDA)-adhered multi-layer graphene oxide (GO) encapsulated silica nanoparticles (SNs). It is demonstrated that compared with traditional SCPs, the designed particles possess brighter and more vibrant structural colors, and no complicated modification is required during the functionalization process due to the abundant inherent functional groups of GO. The resultant SCPs are verified to be capable for direct hybridization chain reaction and multiplexed nucleic acid assays. These properties indicate the promising prospects of our designed SCPs.

Bioinspired Multiple Stimuli-Responsive Optical Microcapsules Enabled by Microfluidics

Optical microcapsules encapsulating optical materials inside a symmetric spherical confinement are significant elements for the construction of optical units and the integration of optical arrays. However, the multiple stimuli-responsive characteristic of optical microcapsules still remains a challenge due to the insuperable physical barrier between the optical material core and the outside shell and the lack of effective mechanisms to trigger the dynamic switch of the encapsulated optical materials. Inspired by the dual-mode optical modulation of chameleon skins, a novel biomimetic binary optical microcapsule that combines the visible light reflection of chiral nematic liquid crystals and photoluminescence emission of rare-earth complexes is assembled by microfluidic emulsification and interfacial polymerization. The reflected color, fluorescent intensity, and size of the optical microcapsules are facilely controlled in the microfluidic chip by adjusting the composition and flow rate of the injected fluids. Most importantly, the biomimetic binary optical microcapsules demonstrate three reversible responsive behaviors, thermotropic reflection evolution, temperature-dependent fluorescence emission, and Fredericks electro-optical response. The bioinspired multiple stimuli-responsive optical microcapsules enabled by microfluidics provide a templated strategy to manufacture the next generation of intelligent optical units and to achieve the dynamic response of hybrid photonic devices.

Colloidal assembly in droplets: structures and optical properties

Colloidal assembly in emulsion drops provides fundamental tools for studying optimum particle arrangement under spherical confinement and practical means for producing photonic microparticles. Recent progress has revealed that energetically favored cluster configurations are different from conventional supraballs, which could enhance optical performance. This paper reviews state-of-the-art emulsion-templated colloidal clusters, and particularly focuses on recently reported novel structures such as icosahedral, decahedral, and single-crystalline face-centered cubic (fcc) clusters. We classify the clusters according to the number of component particles as small (N < O(10²)), medium (O(10²) ≤N≤O(10⁴)), and large (N≥O(10⁵)). For each size of clusters, we discuss the detailed structures, mechanisms of cluster formation, and optical properties and potential applications. Finally, we outline current challenges and questions that require further investigation.

Bioinspired MXene-integrated colloidal crystal arrays for multichannel bioinformation coding

Information coding strategies are becoming increasingly crucial due to the storage demand brought by the information explosion. In particular, bioinformation coding has attracted great attention for its advantages of excellent storage capacity and long lifetime. Herein, we present an innovative bioinspired MXene-integrated photonic crystal (PhC) array for multichannel bioinformation coding. PhC arrays with similar structure to Stenocara beetle's back are utilized as the substrate, exhibiting properties of high throughput and stability. MXene nanosheets are further integrated on the PhC array's substrate with the assistance of the adhesion capacity of mussel-inspired dopamine (DA). Benefitting from their fluorescence resonance energy transfer effect, MXene nanosheets can quench the fluorescence signals of quantum dot (QD) modified DNA probes unless the corresponding targets exist. Additionally, these black MXene nanosheets can enhance the contrast of structural color. In this case, the encrypted information can be easily read out by simply observing the fluorescence signal of DNA probes. It is demonstrated that this strategy based on bioinspired MXene-integrated PhC arrays can realize high-throughput information encoding and encryption, which opens a chapter of bioinformation coding.

Microorganism@UiO-66-NH2 Composites for the Detection of Multiple Colorectal Cancer-Related microRNAs with Flow Cytometry

High-throughput analyses of multitarget markers can facilitate rapid and accurate clinical diagnosis. Suspension array assays, a flow cytometry-based analysis technology, are among some of the most promising multicomponent analysis methods for clinical diagnostics and research purposes. These assays are appropriate for examining low-volume, complex samples having trace amounts of analytes due to superior elimination of background. Physical shape is an important and promising code system, which uses a set of visually distinct patterns to identify different assay particles. Here, we presented a morphology recognizable suspension arrays based on the microorganisms with different morphologies. In this study, UiO-66-NH₂ (UiO stands for University of Oslo) metal-organic frameworks (MOFs), was wrapped on the microorganism surface to form an innovative class of microorganism@UiO-66-NH₂ composites for suspension array assays. The use of microorganisms endowed composites barcoding ability with their different morphology and size. Meanwhile, the UiO-66-NH₂ provided a stable rigid shell, large specific surface area, and metal(IV) ions with multiple binding sites, which could simplify the protein immobilization procedure and enhance detection sensitivity. With this method, simultaneous detection of three colorectal cancer-related microRNA (miRNA), including miRNA-21, miRNA-17, and miRNA-182, could be easily achieved with femtomolar sensitivity by using a commercial flow cytometer. The synergy between microorganisms and MOFs make the composites a prospective barcoding candidate with excellent characteristics for multicomponent analysis, offering great potential for the development of high throughput and accurate diagnostics.

Multiplexed Luminescence Oxygen Channeling Immunoassay Based on Dual-Functional Barcodes with a Host-Guest Structure: A Facile and Robust Suspension Array Platform

The development of a powerful immunoassay platform with capacities of both simplicity and high multiplexing is promising for disease diagnosis. To meet this urgent need, for the first time, a multiplexed luminescent oxygen channeling immunoassay (multi-LOCI) platform by implementation of LOCI with suspension array technology is reported. As the microcarrier of the platform, a unique dual-functional barcode with a host-guest structure composed of a quantum dot host bead (QDH) and LOCI acceptor beads (ABs) is designed, in which QDH provides function of high coding capacity while ABs facilitate the LOCI function. The analytes bridge QDH@ABs and LOCI donor beads (DBs) into a close proximity, forming a QDH@ABs-DBs "host-guest-satellite" superstructure that generates both barcode signal from QDH and LOCI signal induced by singlet oxygen channeling between ABs and DBs. Through imaging-based decoding, different barcodes are automatically distinguished and colocalized with LOCI signals. Importantly, the assay achieves simultaneous detection of multiple analytes within one reaction, simply by following a "mix-and-measure" protocol without the need for tedious washing steps. Furthermore, the multi-LOCI platform is validated for real sample measurements. With the advantages of robustness, simplicity, and high multiplexing, the platform holds great potential for the development of point-of-care diagnostics.

Colloidal Crystals from Microfluidics

Colloidal crystals are of great interest to researchers because of their excellent optical properties and broad applications in barcodes, sensors, displays, drug delivery, and other fields. Therefore, the preparation of high quality colloidal crystals in large quantities with high speed is worth investigating. After decades of development, microfluidics have been developed that provide new choices for many fields, especially for the generation of functional materials in microscale. Through the design of microfluidic chips, colloidal crystals can be prepared controllably with the advantages of fast speed and low cost. In this Review, research progress on colloidal crystals from microfluidics is discussed. After summarizing the classifications, the generation of colloidal crystals from microfluidics is discussed, including basic colloidal particles preparation, and their assembly inside or outside of microfluidic devices. Then, applications of the achieved colloidal crystals from microfluidics are illustrated. Finally, the future development and prospects of microfluidic-based colloidal crystals are summarized.

Label-Free Quantifications of Multiplexed Mycotoxins by G-Quadruplex Based on Photonic Barcodes

Multiplexed quantification of mycotoxins is of great significance in food safety. Here, novel photonic crystal (PhC) barcodes with G-quadruplex aptamer encapsulated for label-free multiplex mycotoxins quantification are developed. The probes are immobilized on PhC barcodes to form a molecular beacon (MB), which contains the sequences of mycotoxin aptamers and a G-quadruplex. In the presence of the target, the hairpin structure of MB would open and the region of the G-quadruplex is exposed, which subsequently combines with Thioflavin T (ThT) to produce fluorescence. The relative fluorescence intensity increased as the mycotoxins concentration increased in a linear range from 1.0 pg/mL to 100 ng/mL. Moreover, the multiplexed mycotoxins quantification could be achieved by tuning the structural color of the PhC barcodes. We demonstrate that this method with high accuracy and specificity for multiplexed detection of mycotoxins, with the sensitivity of the detection as low as 0.70 pg/mL. Our results show that G-quadruplex-encapsulated PhC barcodes offer a novel simple and label-free pathway toward the multiplex screen assay of mycotoxins for food safety.

Responsive principles and applications of smart materials in biosensing

Biosensing is a rising analytical field for detection of biological indicators using transducing systems. Smart materials can response to external stimuli, and translate the stimuli from biological domains into signals that are readable and quantifiable. Smart materials, such as nanomaterials, photonic crystals and hydrogels have been widely used for biosensing purpose. In this review, we illustrate the incorporation of smart materials in biosensing systems, including the design of responsive materials, their responsive mechanism of biosensing, and their applications in detection of four types of common biomolecules (including glucose, nucleic acids, proteins, and enzymes). In the end, we also illustrate the current challenges and prospective of using smart materials in biosensing research fields.

Graphene Oxide-Assisted and DNA-Modulated SERS of AuCu Alloy for the Fabrication of Apurinic/Apyrimidinic Endonuclease 1 Biosensor

Fabrication of high-performance surface-enhanced Raman scattering (SERS) biosensors relies on the coordination of SERS substrates and sensing strategies. Herein, a SERS active AuCu alloy with a starfish-like structure is prepared using a surfactant-free method. By covering the anisotropic AuCu alloy with graphene oxide (GO), enhanced SERS activity is obtained owing to graphene-enhanced Raman scattering and assembly of Raman reporters. Besides, stability of SERS is promoted based on the protection of GO to the AuCu alloy. Meanwhile, it is found that SERS activity of AuCu/GO can be regulated by DNA. The regulation is sequence and length dual-dependent, and short polyT reveals the strongest ability of enhancing the SERS activity. Relying on this phenomenon, a SERS biosensor is designed to quantify apurinic/apyrimidinic endonuclease 1 (APE1). Because of the APE1-induced cycling amplification, the biosensor is able to detect APE1 sensitively and selectively. In addition, APE1 in human serum is analyzed by the SERS biosensor and enzyme-linked immunosorbent assay (ELISA). The data from the SERS method are superior to that from ELISA, indicating great potential of this biosensor in clinical applications.

Bioinspired photonic barcodes for multiplexed target cycling and hybridization chain reaction

Multiplexed detection of microRNA (miRNA) is of great value in clinical diagnosis. Here, a new type of polydopamine (PDA) encapsulated photonic crystal (PhC) barcodes are employed for target-triggering cycle amplification and hybridization chain reaction (HCR) to achieve multiplex miRNA quantification. The PDA-decorated PhC barcodes not only exhibit distinctive structural color for different encoding miRNAs, they also can immobilize biomolecules, allowing subsequent reaction with amino-modified hairpin probes (H1). When the PDA-decorated PhC barcodes are used in assays, target miRNAs can be circularly used to initiate HCR for cycle amplification. Therefore, by tuning the structural colors of the PDA-integrated PhC, the multiplexed miRNA quantification could be realized. We demonstrate that our strategy for multiplexed detection of miRNA is reasonably accurate, reliable and repeatable, with a detection limit as low as 8.0 fM. Our results show that PDA encapsulated PhC barcodes as a novel platform offer a pathway toward the multiplex analysis of low-abundance biomarkers for biomedical assays.

Quantum dots from microfluidics for nanomedical application

Nanomedicine, with its advantages of rapid diagnosis, high sensitivity and high accuracy, has aroused extensive interest of researchers, as the cornerstone of nanomedicine, nanomaterials achieve extra attention and rapid development. Among nanomaterials, quantum dots stand out due to their long fluorescence lifetime and excellent antiphotobleaching performance. At present, quantum dots have been applied to the diagnosis and treatment of diseases and various strategies have been presented to fabricate quantum dots. Microfluidic is one promising strategy since microfluidic device can provide an effective platform for the diagnosis of trace disease markers. In this paper, research progress in the microfluidic synthesis of quantum dots and quantum dot-based nanomedical application is discussed. The classification of quantum dots is firstly introduced, and the researches on quantum dots synthesis based on microfluidic is then mainly described, including the sort, design, preparation of microfluidic synthesis device and its application in synthesis. Nanomedical applications of the quantum dots is especially described and emphasized. The prospects for future development of quantum dots from microfluidic for nanomedical application are finally presented. This article is categorized under: Diagnostic Tools > in vitro Nanoparticle-Based Sensing.

Molybdenum disulfide-integrated photonic barcodes for tumor markers screening

As a new class of two-dimensional (2D) materials, molybdenum disulfide (MoS₂) has huge potential in biomedical area; while its applications in multiplex bioassays are still a challenge. Here, we present novel MoS₂-integrated silica colloidal crystal barcode (SCCB) for multiplex microRNA (miRNA) screening. MoS₂ was adsorbed on SCCBs by electrostatic interaction, and quantum dots (QDs) decorated hairpin probes were coupled on MoS₂ by covalent linkage. As the MoS₂ could quench the QDs of the hairpin probes, they together formed a molecular beacon (MB) structure before the detection. When used in assays, target miRNA could form a double strand with the probe and made QDs keep away from MoS₂ sheets to recovery their fluorescence. Because the released QDs were positively correlated with the concentration of the hybridized nucleic acid, the target miRNAs could be quantified by measuring the fluorescence signal of the QDs on the SCCBs. In addition, by utilizing different MoS₂-integrated structural color encoded SCCBs, multiplexed miRNA quantification could also be realized. Based on this strategy, we have demonstrated that several pancreatic cancer-related miRNAs could be selectivity and sensitivity detected with a detection limit of 4.2 ± 0.3 nM. These features make the MoS₂-integrated SCCB ideal for many potential applications.