Developing highly sensitive and highly selective assays for monitoring heparin levels in blood is required during and after surgery. In previous studies, electrostatic interactions are exploited to recognize heparin and changes in light signal intensity are used to sense heparin. In the present study, we developed a quantum dot (QD) aggregation-based detection strategy to quantify heparin. When cationic micelles and fluorescence QDs modified with anti-thrombin III (AT III) are added into heparin sample solution, the AT III-QDs, which specifically bind with heparin, aggregate around the micelles. The aggregated QDs are recorded by spectral imaging fluorescence microscopy and differentiated from single QDs based on the asynchronous process of blue shift and photobleaching. The ratio of aggregated QD spots to all counted QD spots is linearly related to the amount of heparin in the range of 4.65 × 10 –4 U/mL to 0.023 U/mL. The limit of detection is 9.3 × 10 –5 U/mL (∼0.1 nM), and the recovery of the spiked heparin at 0.00465 U/mL (∼5 nM) in 0.1% human plasma is acceptable.Keywords: aggregation; anti-thrombin III; heparin; quantum dot; single particle; spectral imaging microscopy;

We present a universal and scalable method to fabricate Janus droplets based on evaporation driven liquid–liquid phase separation. In this work, the morphologies and chemical properties of separate parts of the Janus droplets can be flexibly regulated, and more complex Janus droplets (such as core–shell Janus droplets, ternary Janus droplets, and multiple Janus droplets) can be constructed easily.

Mercury severely damages the environment and human health, particularly when it accumulates in the food chain. Methods for the colorimetric detection of Hg2+ have increasingly been developed over the past decade because of the progress in nanotechnology. However, the limits of detection (LODs) of these methods are mostly either comparable to or higher than the allowable maximum level (10 nM) in drinking water set by the US Environmental Protection Agency. In this study, we report a single Au nanoparticle (AuNP)-based colorimetric assay for Hg2+ detection in solution. AuNPs modified with oligonucleotides were fixed on the slide. The fixed AuNPs bound to free AuNPs in the solution in the presence of Hg2+ because of oligonucleotide hybridization. This process was accompanied by a color change from green to yellow as observed under an optical microscope. The ratio of changed color spots corresponded with Hg2+ concentration. The LOD was determined as 1.4 pM, which may help guard against mercury accumulation. The proposed approach was applied to environmental samples with recoveries of 98.3 ± 7.7% and 110.0 ± 8.8% for Yuquan River and industrial wastewater, respectively.

A new simple colorimetric chemosensor for sensitive and selective detection of Cu2+ using polyethyleneimine (PEI)-capped Au nanoparticles (PEI/Au NPs) has been developed. PEI/Au NPs are synthesized by using PEI as reducer without adding nanoparticles seeds and stabilizing agent. Copper ions are captured by the amino groups of the PEI/Au NPs to form an absorbent complex at the surface of PEI/Au NPs, resulting in the color of PEI/Au NPs changing from wine red to purple. Under the optimal conditions, the proposed colorimetric sensor is capable of sensitively and specifically detecting Cu2+ with a detection limit of 0.29 μM and a linear range of 25–300 μM. This method is simple, fast and highly selective for Cu2+ in the presence of high concentrations of other environmentally relevant metal ions because of the great specific coordination between Cu2+ and PEI, which potentially meets the requirement of the detection in real samples. Moreover, addition of EDTA to PEI/Au NPs-Cu2+ recovers the color offering PEI/Au NPs as a promising reversible sensor for practical application.

We develop a method to quantify the quantum dots (QDs) in QD aggregates in aqueous solution by recording the entire process of blue shifting and photobleaching under continuous illumination and utilize this method to detect the biotinylated proteins based on counting the degree of aggregation (DOA).

•Au nanoparticle was firstly used as lectin affinity chromatography (LAC) support.•Reproducibility of LAC is easily achieved by monitoring Au nanoparticle’s LSPR.•Our method has the potential use in on-site quality control of glycoprotein.Fast glycoform analysis is important for quality control of glycoproteins that account for over 40% of the approved biopharmaceuticals. Herein, we realized an Au nanoparticle-based lectin affinity chromatography (LAC) using simple standard laboratory equipment for fast glycoform analysis. Pisum sativum agglutinin (PA), a lectin derived from P. sativum, was covalently conjugated to Au nanoparticles via naturally formed carboxylic groups onto the surface of Au nanoparticles and amino groups of PA. Each model glycoprotein was separated into several fractions including the unbound, weakly bound, modestly bound, and strongly bound glycoforms based on affinity strength of the glycoform toward PA. A single run of Au nanoparticle-based LAC was finished within 18 min, which could be further decreased by centrifuging the mixture of the PA functionalized Au nanoparticles and the glycoproteins at a higher speed. To our knowledge, we are the first to use Au nanoparticles as LAC matrix.

In this paper, we present a novel method to generate ultra-small droplets via volatile component evaporation. By regulating the composition of the binary solvent, the volume ratio of the high saturated vapor pressure component, and the flow rate ratio of the two phases, monodisperse ultra-small water or nonvolatile organic droplets can be formed. This method is flexible, versatile, and compatible with tip-streaming or nanofluidics, and may have potential applications in single molecule assay, colloid synthesis, and block copolymer assembly.

Quantifying carbohydrate–protein (ligand–receptor) interactions is important to understand diverse biological processes and to develop new diagnostic and therapeutic methods. We develop an approach to quantitatively study carbohydrate–protein interactions by Au nanoparticle localized surface plasmon resonance (LSPR) peak position shift at the single particles level. Unlike the previous techniques for single particle LSPR spectral imaging, only the first-order streak of an individual nanoparticle is needed to extract a LSPR spectrum, which has great potential to increase throughput to 500 single particle spectra in each frame. LSPR peak shift of protein modified single Au nanoparticles is found to be a function of its ligand concentration, which can be used to fit the binding constants of the interactions. The moderate interactions of Antithrombin III (AT III) and heparins including low molecular weight heparin (LMWH) are determined as well as the strong interaction of transferrin and antitransferrin and the weak interaction of bovine serum album (BSA) and heparin. The measured binding constants of transferrin to antitransferrin, heparin and LMWH to AT III, and BSA to heparin are (3.0 ± 0.6) × 109 M–1, (3.1 ± 0.3) × 106 M–1, (8.0 ± 0.5) × 105 M–1, and (5.1 ± 0.1) × 103 M–1, respectively, which are in good agreement with the reported values.

Core–shell quantum dots suffer from photobleaching by light at wavelengths longer than their emission wavelengths. That is, QD photobleaching can be triggered by photons with low energies that are insufficient to pump electrons into the conduction band. The most probable reason is that electrons are pumped into a surface state and then nonradiatively decayed as in conventional photobleaching.

We present a miniaturized fuel cell driven by an evaporation pump. The prototype cell shows a net peak current density of 22 mA cm−2 and a net power density of 10.2 mW cm−2, both of which are the highest net values among passive-driven micro-fuel cells.

We develop a method to quantify the quantum dots (QDs) in QD aggregates in aqueous solution by recording the entire process of blue shifting and photobleaching under continuous illumination and utilize this method to detect the biotinylated proteins based on counting the degree of aggregation (DOA).

We present a universal and scalable method to fabricate Janus droplets based on evaporation driven liquid–liquid phase separation. In this work, the morphologies and chemical properties of separate parts of the Janus droplets can be flexibly regulated, and more complex Janus droplets (such as core–shell Janus droplets, ternary Janus droplets, and multiple Janus droplets) can be constructed easily.

Core–shell quantum dots suffer from photobleaching by light at wavelengths longer than their emission wavelengths. That is, QD photobleaching can be triggered by photons with low energies that are insufficient to pump electrons into the conduction band. The most probable reason is that electrons are pumped into a surface state and then nonradiatively decayed as in conventional photobleaching.