"Plug and Play" logic gate construction based on chemically triggered fluorescence switching of gold nanoparticles conjugated with Cy3-tagged aptamer.

Gold nanoparticles (AuNPs) conjugated with Cy3-tagged aptamer which can specifically recognize chloramphenicol (CAP) (referred to as AuNPs-AptCAP) are described. CAP can trigger the configuration change of CAP binding aptamer, and thus switching the fluorescence of AuNPs-AptCAP through changing the efficiency of the fluorescence resonance energy transfer (FRET) system with Cy3 as donors and AuNPs as recipients. AuNPs-AptCAP exhibits a linear range of CAP concentrations from 26.0 to 277 µg L-1 with a limit of detection of 8.1 µg L-1 when Cy3 was excited at 530 nm and emission was measured at 570 nm. More importantly, AuNPs-AptCAP can be utilized as signal transducers for the build-up of a series of logic gates including YES, PASS 0, INH, NOT, PASS 1, and NAND. Utilizing the principle of a metal ion-mediated fluorescence switch together with a strong metal ion chelator, the fluorescence of AuNPs-AptCAP could be modulated by adding metal ions and EDTA sequentially. Therefore, a "Plug and Play" logic system based on AuNPs-AptCAP has been realized by simply adding other components to create new logic functions. This work highlights the advantages of simple synthesis and facile fluorescence switching properties, which will provide useful knowledge for the establishment of molecular logic systems. Graphical abstract.

Facile synthesis and functionalization of color-tunable Ln3+-doped KGdF4 nanoparticles on a microfluidic platform.

Hyaluronic acid (HA)-functionalized lanthanide-doped KGdF4 nanoparticles were synthesized through two steps on a microfluidic platform. This microfluidic synthesis method allows better control of experimental conditions with lower labor and energy input than traditional beaker synthesis methods for large-scale production of nanoparticles with higher uniformity. First, Ln3+-doped KGdF4 nanoparticles were ultrafast (in minutes) and continuously synthesized using a four-inlets microfluidic chip at room temperature. Then, HA is continuously functionalized on the surface of Ln3+-doped KGdF4 nanoparticles using a T-shape chip through electrostatic adsorption. The synthesized nanoparticles show good uniformity, high biocompatibility, targeted cellular uptake, photoluminescence (PL) and magnetic resonance (MR) properties. This work highlights the potential of microfluidic platform for the development of multifunctional nanoparticles in biomedicine.

Recent advances in microfluidic technology for manipulation and analysis of biological cells (2007-2017).

The pivotal role of microfluidic technology in life science and biomedical research is now widely recognized. Indeed, microfluidics as a research tool is unparalleled in terms of its biocompatibility, robustness, efficient reagent consumption, and controlled fluidic, surface, and structure environments. The controlled environments are essential in assessing the complex behavior of cells in response to microenvironmental cues. The strengths of microfluidics also reside in its amenability to integration with other analytical platforms and its capacity for miniaturization, parallelization and automation of biochemical assays. Following previous review on the applications of microfluidic devices for cell-based assays in 2006, we have monitored the progress in the field and summarized the advances in microfluidic technology from 2007 to 2017, with a focus on microfluidics development for applications in cell manipulation, cell capture and detection, and cell treatment and analysis. Moreover, we highlighted novel commercial microfluidic products for biomedical and clinical purposes that were introduced in the review period. Thus, this review provides a comprehensive source for recent developments in microfluidics and presents a snapshot of its remarkable contribution towards basic biomedical research and clinical science. We recognize that although enormous amounts of evidence have reinforced the promise of microfluidic technology across diverse applications, much remains to be done to realize its full potential in mainstream biomedical science and clinical practice.

A ratiometric fluorescent core-shell nanoprobe for sensing and imaging of zinc(II) in living cell and zebrafish.

A zinc(II)-responsive ratiometric fluorescent core-shell nanoprobe (referred to as QPNPs) is described. It consist of an optimized combination of an internal reference dye (TBAP) encapsulated in the core, and a Zn(II)-specific indicator dye (PEIQ) in the shell. The nanoprobe was synthesized via single-step graft copolymerization induced by tert-butyl hydroperoxide at 80 °C. QPNPs exhibit a well-defined core-shell nanostructure and well-resolved dual emissions after photoexcitation at 380 nm. After exposure to Zn(II), the QPNPs display a green fluorescence peaking at ~500 nm that increases with the concentration of Zn(II), while the pink fluorescence of the porphine-derived reference dye peaking at ~650 nm remains unchanged. This results in color change from pink to green and thus enables Zn(II) to be detected both spectroscopically and with bare eyes. Zn(II) can be quantified with a 3.1 nM detection limit. The core-shell structured nanoprobe was also applied to real-time imaging of Zn(II) in living HeLa cells and in zebrafish. This work establishes a reliable approach to synthesize ratiometric fluorescent nanoprobes. It enables such nanoprobes to be prepared also by those not skilled in nanomaterial synthesis. Graphical abstract A zinc(II)-responsive core-shell nanoprobe (referred to as QPNP) is synthesized via single-step graft copolymerization. Zn(II) can be quantitated with a 3.1 nM detection limit by the QPNPs through ratiometric fluorescence strategy (PEIQ as the Zn(II) indicator and TBAP as the reference dye).

A fast and low-cost microfabrication approach for six types of thermoplastic substrates with reduced feature size and minimized bulges using sacrificial layer assisted laser engraving.

Since polydimethylsiloxane (PDMS) is notorious for its severe sorption to biological compounds and even nanoparticles, thermoplastics become a promising substrate for microdevices. Although CO2 laser engraving is an efficient method for thermoplastic device fabrication, it accompanies with poor bonding issues due to severe bulging and large feature size determined by the diameter of laser beam. In this study, a low-cost microfabrication method is proposed by reversibly sealing a 1 mm thick polymethylmethacrylate (PMMA) over an engraving substrate to reduce channel feature size and minimize bulges of laser engraved channels. PMMA, polycarbonate (PC), polystyrene (PS), perfluoroalkoxy alkane (PFA), cyclic-olefin polymers (COP) and polylactic acid (PLA) were found compatible with this sacrificial layer assisted laser engraving technique. Microchannel width as small as ∼40 µm was attainable by a laser beam that was 5 times larger in diameter. Bulging height was significantly reduced to less 5 µm for most substrates, which facilitated leak proof device bonding without channel deformation. Microdevices with high aspect ratio channels were prepared to demonstrate the applicability of this microfabrication method. We believe this fast and low-cost fabrication approach for thermoplastics will be of interest to researchers who have encountered problem with polydimethylsiloxane based microdevices in their applications.

Controllable synthesis of functional nanoparticles by microfluidic platforms for biomedical applications - a review.

Nanoparticles have drawn significant attention in biomedicine due to their unique optical, thermal, magnetic and electrical properties which are highly related to their size and morphologies. Recently, microfluidic systems have shown promising potential to modulate critical stages in nanosynthesis, such as nucleation, growth and reaction conditions so that the size, size distribution, morphology, and reproducibility of nanoparticles are optimized in a high throughput manner. In this review, we put an emphasis on a decade of developments of microfluidic systems for engineering nanoparticles in various applications including imaging, biosensing, drug delivery, and theranostic applications.

Grafting polyethylenimine with quinoline derivatives for targeted imaging of intracellular Zn(2+) and logic gate operations.

In this study, a highly sensitive and selective fluorescent Zn(2+) probe which exhibited excellent biocompatibility, water solubility, and cell-membrane permeability, was facilely synthesized in a single step by grafting polyethyleneimine (PEI) with quinoline derivatives. The primary amino groups in the branched PEI can increase water solubility and cell permeability of the probe PEIQ, while quinoline derivatives can specifically recognize Zn(2+) and reduce the potential cytotoxicity of PEI. Basing on fluorescence off-on mechanism, PEIQ demonstrated excellent sensing capability towards Zn(2+) in absolute aqueous solution, where a high sensitivity with a detection limit as low as 38.1nM, and a high selectivity over competing metal ions and potential interfering amino acids, were achieved. Inspired by these results, elementary logic operations (YES, NOT and INHIBIT) have been constructed by employing PEIQ as the gate while Zn(2+) and EDTA as chemical inputs. Together with the low cytotoxicity and good cell-permeability, the practical application of PEIQ in living cell imaging was satisfactorily demonstrated, emphasizing its wide application in fundamental biology research.

Design of Multiple Logic Gates Based on Chemically Triggered Fluorescence Switching of Functionalized Polyethylenimine.

In this study, two new functionalized polyethylenimine (PEI), PEIR and PEIQ, have been synthesized by covalently conjugating rhodamine 6G (R6G) or 8-chloroacetyl-aminoquinoline (CAAQ) and have been investigated for their sensing capabilities toward metal ions and anions basing on fluorescence on-off and off-on mechanisms. When triggered by protons, metal ions, or anions, functionalized PEIs can behave as a fluorescence switch, leading to a multiaddressable system. Inspired by these results, functionalized PEI-based logic systems capable of performing elementary logic operations (YES, NOT, NOR, and INHIBIT) and integrative logic operations (OR + INHIBIT) have been constructed by observing the change in the fluorescence with varying the chemical inputs such as protons, metal ions, and anions. Due to its characteristics, such as high sensitivity and fast response, developing functionalized PEI as a new material to perform logic operations may pave a new avenue to construct the next generation of molecular devices with better applicability for biomedical research.

Deposition of gadolinium onto the shell structure of micelles for integrated magnetic resonance imaging and robust drug delivery systems.

Selective deposition of Gd(iii) ions onto the shell structure of complex micelles was achieved to yield Gd decorated hybrid micelles for integrated magnetic resonance imaging and drug delivery. The complex micelles were engineered by the hydrophilic-hydrophobic self-assembly of two kinds of amphiphilic polymers, pluronic F127 and a peptide-amphiphile (PA), via a facile, environmentally benign strategy. These core-shell complex micelles provide a robust multifunctional platform for theranostic applications. The hydrophobic core of micelles allows us to compartmentalize anti-cancer drugs, while the shell structure with a mixed poly(ethylene-oxide) (PEO) and peptide composition provides chelation capacity for the MRI contrast agent Gd(iii). The nanoscaled hybrid micelles are not only developed to address the challenges of small molecular Gd(iii)-chelates, but also be integrated with the capability of anticancer drug delivery for tumor therapy. More importantly, a synergy effect was observed such that the coordination effect of Gd(iii) with the shell enhanced the micellar stability and retarded the DOX release behavior. In vitro and in vivo experiments of MRI contrast enhancement and therapy clearly evidenced that the DOX loaded hybrid micelles can serve as efficient theranostic agents.

Synthesis, characterization and biomedical application of multifunctional luminomagnetic core-shell nanoparticles.

It has been well-established that nanomaterials provide a robust framework into which two or more functional moieties can be integrated to offer multifunctional and synergetic applications. We report here the facile synthesis and systematical investigation of the luminomagnetic core-shell nanoparticles (NPs) with the magnetic Fe3O4 core coated with a silica shell incorporating fluorescent [Ru(bpy)3](2+). The luminomagnetic NPs were monodisperse and spherical in shape with a diameter of 60±10 nm. The luminomagnetic NPs possessed not only the desirable optical signature of Ru(bpy)3(2+) but also the distinctive magnetic profile of Fe3O4, where a strong red-orange emission and the super-paramagnetic characteristics with the saturation magnetization values ca. 10 emu/g were observed for the luminomagnetic NPs. As revealed by Alamar blue assay and flow cytometry analysis, the Fe3O4 NPs decrease the cell viability of HepG2 by ca. 10%, while an increase by ca. 10% on HepG2 cell proliferation was revealed after the silica shell was coated onto Fe3O4 NPs, suggesting that the silica shell serves as a protective layer to increase the biocompatibility of the luminomagnetic NPs. Confocal laser scanning microscopy, transition electron microscopy and magnetic resonance (MR) images confirmed that the luminomagnetic NPs can enter into the interiors of HepG2 cells without damage, highlighting their capabilities for simultaneous optical fluorescence imaging and T2 MR imaging. Taking advantage of versatility of silica shell towards different surface modification protocols, the luminomagnetic NPs were successfully functionalized with epidermal growth factor receptor (EGFR) antibody for HepG2 cell recognition. All the results illustrated that the luminomagnetic NPs should be a potential candidate for future cancer diagnosis and therapy.

A microfluidic linear node array for the study of protein-ligand interactions.

We have developed a microfluidic device for the continuous separation of small molecules from a protein mixture and demonstrated its practical use in the study of protein-ligand binding, a crucial aspect in drug discovery. Our results demonstrated dose-dependent binding between bovine serum albumin (BSA) and its small-molecule site marker, Eosin Y (EY), and found that the binding reached a plateau when the BSA : EY ratio was above 1, which agreed with the eosin binding capacity of BSA reported in literature. By streamline control using a combination of two fundamental building blocks (R and L nodes) with a microdevice operated at a high flow rate (up to 1300 µL h(-1)), a solution barrier was created to "filter" off protein/protein-ligand complexes such that the small unbound molecules were isolated and quantified easily. The percentage decrease of small molecules with increasing protein concentration indicated the presence of binding events. Several fluorophores with different molecular weights were used to test the performance of the microfluidic "filter", which was tunable by 1) the total flow rate, and/or 2) the flow distribution ratio between the two device inlets; both were easily controllable by changing the syringe pump settings. Since the microdevice was operated at a relatively high flow rate, aliquots were easily recovered from the device outlets to facilitate off-chip detection. This microfluidic design is a novel and promising tool for preliminary drug screening.

Discovery of a benzofuran derivative (MBPTA) as a novel ROCK inhibitor that protects against MPP⁺-induced oxidative stress and cell death in SH-SY5Y cells.

Parkinson disease (PD) is a neurodegenerative disease with multifactorial etiopathogenesis. The discovery of drug candidates that act on new targets of PD is required to address the varied pathological aspects and modify the disease process. In this study, a small compound, 2-(5-methyl-1-benzofuran-3-yl)-N-(5-propylsulfanyl-1,3,4-thiadiazol-2-yl) acetamide (MBPTA) was identified as a novel Rho-associated protein kinase inhibitor with significant protective effects against 1-methyl-4-phenylpyridinium ion (MPP(+))-induced damage in SH-SY5Y neuroblastoma cells. Further investigation showed that pretreatment of SH-SY5Y cells with MBPTA significantly suppressed MPP(+)-induced cell death by restoring abnormal changes in nuclear morphology, mitochondrial membrane potential, and numerous apoptotic regulators. MBPTA was able to inhibit MPP(+)-induced reactive oxygen species (ROS)/NO generation, overexpression of inducible NO synthase, and activation of NF-κB, indicating the critical role of MBPTA in regulating ROS/NO-mediated cell death. Furthermore, MBPTA was shown to activate PI3K/Akt survival signaling, and its cytoprotective effect was abolished by PI3K and Akt inhibitors. The structural comparison of a series of MBPTA analogs revealed that the benzofuran moiety probably plays a crucial role in the anti-oxidative stress action. Taken together, these results suggest that MBPTA protects against MPP(+)-induced apoptosis in a neuronal cell line through inhibition of ROS/NO generation and activation of PI3K/Akt signaling.

A novel dual-emission ratiometric fluorescent nanoprobe for sensing and intracellular imaging of Zn2+.

The integration of unique characteristics of nanomaterials with highly specific recognition elements, such as biomolecules and organic molecules, are the foundation of many novel nanoprobes for bio/chemical sensing and imaging. In the present report, branched polyethylenimine (PEI) was grafted with 8-chloroacetyl-aminoquinoline to synthesize a water-soluble and biocompatible quinoline-based Zn(2+) probe PEIQ. Then the PEIQ was covalently conjugated to [Ru(bpy)3](2+)-encapsulated SiNPs to obtain the ratiometric fluorescence nanoprobe which exhibits a strong fluorescence emission at 600 nm and a negligible fluorescence emission at 500 nm in the absence of Zn(2+) upon a single wavelength excitation. After the addition of different amounts of Zn(2+), the fluorescence intensity at 500 nm increased continuously while the fluorescence intensity at 600 nm remained stable, thus changing the dual emission intensity ratios and displaying continuous color changes from red to green which can be clearly observed by the naked eye. The nanoprobe exhibits good water dispersivity, biocompatibility and cell permeability, high selectivity over competing metal ions, and high sensitivity with a detection limit as low as 0.5 µM. Real-time imaging of Zn(2+) in A549 cells has also been realized using this novel nanoprobe.

Single layer linear array of microbeads for multiplexed analysis of DNA and proteins.

In this study, a microfluidic platform was developed to generate single layer, linear array of microbeads for multiplexed high-throughput analysis of biomolecules. The microfluidic device is comprised of eight microbead-trapping units, where microbeads were immobilized in a linear array format by the exertion of a negative pressure in the control channel connected to each sieving microstructure. Multiplexed assays were achieved by using a mixture of different spectrally-encoded microbeads functionalized with specific probes, followed by on-chip reaction and detection. The microfluidic-based microbeads array platform was employed for multiplexed analysis of DNA and proteins, as demonstrated by the simultaneous discrimination of four HPV genotypes and the parallel detection of six different proteins. Compared with the off-chip protocols, the on-chip analysis exhibited better reaction efficiency, higher sensitivity and wider linear detection range. Visual inspection and identification of functionalized microbeads were facilitated by the single layer arrangement of microbeads so that accurate data acquisition can be performed during the detection process.

Microfluidics study of intracellular calcium response to mechanical stimulation on single suspension cells.

A microfluidic microdevice was developed to exert mechanical stimulation on an individual suspension cell for mechanosensation research. In this microfluidic chip, an individual cell was isolated from a population of cells, and trapped in a microchannel with a compressive component made of a deflectable membrane. The mechanosensation of HL60 cells (leukemic cells) was studied using this chip, and the results showed that mechanical stimulations could trigger extracellular calcium to flow into HL60 cells through ion channels on cell membranes. The tension on individual HL60 cells exerted by the microdevice was showed large variations in the threshold of mechanosensation activation. In contrast to previous reports using patch clamp technique, there was little influence of cytoskeleton interruption on HL60 cell mechanosensation triggered by whole-cell compression. Additionally, two functional units were integrated in one chip for carrying out mechanosensation study in parallel, where HL60 cells (leukemic cells) and Jurkat cells (lymphocytes) were shown to respond to mechanical stimulation with different kinetics. The results demonstrated that the microfluidic device provides a novel approach to investigating the mechanosensation of single suspension cells in high-throughput.

Screen printing of solder resist as master substrates for fabrication of multi-level microfluidic channels and flask-shaped microstructures for cell-based applications.

Although silicon technology can be adopted for the fabrication of microfluidic devices with high precision, the capital and operating costs for such technology is often prohibitively expensive. In recent years, many alternative methods have been advocated to reduce the cost of microfabrication but often with reduced qualities in many important features, such as channel resolution, surface smoothness and aspect ratio. In this study, we have developed a microfabrication method that retains high channel quality and aspect ratio by exploring a rarely used solder resist material in combination with screen printing technique to generate masters where PDMS-based microfluidic devices could be fabricated by replica molding from the masters. Using screen printing, different channel heights from 5 to 60 µm on the master were prepared by varying mesh density, controlling solder resist viscosity, and/or adjusting the off-contact gap between a mesh and a substrate, while the entire master fabrication process was completed within 3 h. This simple, low-cost method could generate fine channel features (50 µm) and high aspect ratio (2:1) structures. Microfluidic devices with multi-level structure could be fabricated by multi-steps photolithography using this approach. Moreover, the properties of solder resist enabled the fabrication of flask-shaped well structures by controlled partial exposure and development in a single-step of photolithography, which was potentially used as cell holding reservoirs for cell quantification and cell culture. We believe this fabrication method can be easily adopted by other laboratories to conduct microfluidic researches without specialized equipment.

Integrated sieving microstructures on microchannels for biological cell trapping and droplet formation.

We have developed a single step microfabrication method to prepare constriction microstructures on a PCB master by controlling the etching time of two microchannels separated by a finite distance that is easily attainable using imagesetters widely available in the printing industry. PDMS replica of the constriction structures present sieving microstructures (microsieves) that could be used for size-dependent trapping of microspheres, biological cells and the formation of water-in-oil droplets.

Multienzyme-nanoparticles amplification for sensitive virus genotyping in microfluidic microbeads array using Au nanoparticle probes and quantum dots as labels.

A novel microfluidic device with microbeads array was developed and sensitive genotyping of human papillomavirus was demonstrated using a multiple-enzyme labeled oligonucleotide-Au nanoparticle bioconjugate as the detection tool. This method utilizes microbeads as sensing platform that was functionalized with the capture probes and modified electron rich proteins, and uses the horseradish peroxidase (HRP)-functionalized gold nanoparticles as label with a secondary DNA probe. The functionalized microbeads were independently introduced into the arrayed chambers using the loading chip slab. A single channel was used to generate weir structures to confine the microbeads and make the beads array accessible by microfluidics. Through "sandwich" hybridization, the enzyme-functionalized Au nanoparticles labels were brought close to the surface of microbeads. The oxidation of biotin-tyramine by hydrogen peroxide resulted in the deposition of multiple biotin moieties onto the surface of beads. This deposition is markedly increased in the presence of immobilized electron rich proteins. Streptavidin-labeled quantum dots were then allowed to bind to the deposited biotin moieties and displayed the signal. Enhanced detection sensitivity was achieved where the large surface area of Au nanoparticle carriers increased the amount HRP bound per sandwiched hybridization. The on-chip genotyping method could discriminate as low as 1fmol/L (10zmol/chip, SNR>3) synthesized HPV oligonucleotides DNA. The chip-based signal enhancement of the amplified assay resulted in 1000 times higher sensitivity than that of off-chip test. In addition, this on-chip format could discriminate and genotype 10copies/µL HPV genomic DNA using the PCR products. These results demonstrated that this on-chip approach can achieve highly sensitive detection and genotyping of target DNA and can be further developed for detection of disease-related biomolecules at the lowest level at their earliest incidence.

Whole gene amplification and protein separation from a few cells.

Despite the growing interest to explore untapped microbial gene and protein diversity, no single platform has been able to acquire both gene and protein information from just a few cells. We present a microfluidic system that simultaneously performs on-chip capillary electrophoresis for protein analysis and whole genome amplification (WGA), and we demonstrate this by doing both for the same cohort of cyanobacterial cells. This technology opens avenues for studying protein profiles of precious environmental microbial samples and simultaneously accessing genomic information based on WGA.

Particle sorting using a porous membrane in a microfluidic device.

Porous membranes have been fabricated based on the development of the perforated membrane mold [Y. Luo and R. N. Zare, Lab Chip, 2008, 8, 1688-1694] to create a single filter that contains multiple pore sizes ranging from 6.4 to 16.6 µm inside a monolithic three-dimensional poly(dimethylsiloxane) microfluidic structure. By overlapping two filters we are able to achieve smaller pore size openings (2.5 to 3.3 µm). This filter operates without any detectable irreversible clogging, which is achieved using a cross-flow placed in front of each filtration section. The utility of a particle-sorting device that contains this filter is demonstrated by separating polystyrene beads of different diameters with an efficiency greater than 99.9%. Additionally, we demonstrate the effectiveness of this particle-sorting device by separating whole blood samples into white blood cells and red blood cells with platelets.