Shenna Chen

Multiplex plasmonic sensor for detection of different metal ions based on a single type of gold nanorod.

In this paper, a label-free multiplex plasmonic sensor has been developed to selectively determine different metal ions including Fe(3+), Hg(2+), Cu(2+), and Ag(+) ions based on a single type of gold nanorod (GNR). Under proper conditions, these metal ions can react with GNRs, resulting in changes of nanostructure and composition. The determination of Fe(3+), Hg(2+), Cu(2+), and Ag(+) ions is therefore readily implemented due to changes of longitudinal plasmon wavelength (LPW) of nanorods. Moreover, the GNR-based assay can not only determine all four kinds of metal ions successively but also can detect which of any one or several kinds of metal ions. This assay is sensitive to detect Fe(3+), Hg(2+), Cu(2+), and Ag(+) as low as 10(-6), 10(-8), 10(-10), and 10(-8) M, respectively. Importantly, the special nanostructure and composition of the nanorods are induced by these metal ions, which allow this sensor to maintain high selectivity to determine these metal ions. This nanosensor abrogates the need for complicated chemosensors or sophisticated equipment, providing a simple and highly selective detection platform.

Enhanced fluorescence of chitosan based on size change of micelles and application to directly selective detecting Fe3+ in humanserum

In this paper, we have developed an approach to significantly enhance fluorescence of chitosan by simply heated the inherently low fluorescent chitosan aqueous solution. Enhanced blue fluorescence of chitosan solution was observed as originated from the formation of small size of chitosan micelle after long time heated. The fluorescence of chitosan micelles was quenched and recovered when Fe³⁺ ions were combined and released from chitosan micelles. Therefore, chitosan without modification of functional groups can recognize Fe³⁺ with very high selectivity. As a result, a new fluorescence sensor for sensitively detecting Fe³⁺ ion based on the change of chitosan micelles sizes was subsequently fabricated. This enhanced fluorescence enables the chitosan sensor to be sensitive to low concentrations of Fe³⁺, and it is linear responsive in the range of 1.96×10⁻⁸ to 2.00×10⁻⁵ M. Importantly, this novel sensor may be applied in human serum for direct detection of Fe³⁺ ion without sample pretreatment. Analysis of 5 samples of human serum shows that the average concentration of Fe³⁺ is 26.95 μM, which is consistent with the results determined by other methods. Moreover, the advantage of chitosan-based assay is that Fe³⁺ rather than Fe²⁺ in human serum can be directly measured, avoiding costly, time-consuming and complex process.

Ultrasensitive Determination of Copper in Complex Biological Media Based on Modulation of Plasmonic Properties of Gold Nanorods

Accurate determination of copper in complex biological media such as cells is quite difficult, and an analytical strategy based on copper-modulated formation of core-shell gold nanorods is described. Selective and label-free sensing can be achieved by measuring the change in the localized surface plasmon resonance absorption. The technique can determine trace amounts of copper in human serum, urine, and red blood cells without or with minimal sample pretreatment. The Cu detection limits are 20.67 μM in human serum, 0.193 μM in human urine, and 3.09 × 10(-16) g in a single cell. The advantages of the technique are the high selectivity, simple or no sample pretreatment, and label free. Boasting a practical detection limit down to 2 fM, only 10(3) red blood cells are needed to conduct the analysis and the technique may be extended to the detection of trace amounts of copper in a single cell.

Carbon dots as a fluorescent probe for label-free detection of physiological potassium level in human serum and red blood cells.

A unique photoluminescence carbon dots (CDs) with larger size were prepared by microwave-assisted method. Complex functional groups on the surface of the CDs facilitate the nanoparticles to form affinity with some metal ions. Taking advantage of the effective fluorescence quenching effect of K(+), a highly sensitive CD-based fluorescence analytical system for label-free detection of K(+) with limit of detection (LOD) 1.0×10(-12) M was established. The concentrations of potassium ion in biological samples such as human serum are usually found at millimolar levels or even higher. The proposed method begins with a substantial dilution of the sample to place the K(+) concentration in the dynamic range for quantification, which covers 3 orders of magnitude. This offers some advantages: the detection of K(+) only needs very small quantities of biological samples, and the dilution of samples such as serum may effectively eliminate the potential interferences that often originate from the background matrix. The determined potassium levels were satisfactory and closely comparable with the results given by the hospital, indicating that this fluorescent probe is applicable to detection of physiological potassium level with high accuracy. Compared with other relative biosensors requiring modified design, bio-molecular modification or/and sophisticated instruments, this CD-based sensor is very simple, cost-effective and easy detection, suggesting great potential applications for successively monitoring physiological potassium level and the change in biological system.

Detection of Fe(III) and bio-copper in human serum based on fluorescent AuAg nanoclusters

In this study, a fluorescence assay for the successive determination of Fe3+ and Cu2+ ions based on the quenching fluorescence of composite AuAg nanoclusters (AuAg NCs) was developed. Using this binary fluorescence sensor, the Fe(III) level in a human serum sample can be directly detected without pretreatment. After the nitrification of human serum, the bio-copper level in human serum may be measured with a quick response. Human serum samples were analyzed, and the average concentration of Fe(III) and bio-copper were found to be 2.33 × 10−5 and 2.91 × 10−5 M, respectively. This assay was not only sensitively responsive to blood iron(III) but also to serum copper, suggesting significant potential applications for successively monitoring the Fe(III) and bio-copper levels, and their changes during the progression of a biological process.

Synthesis of biocompatible AuAgS/Ag2S nanoclusters and their applications in photocatalysis and mercury detection

In this paper, a facile approach for preparation of AuAgS/Ag2S nanoclusters was developed. The unique AuAgS/Ag2S nanoclusters capped with biomolecules exhibit interesting excellent optical and catalytic properties. The fluorescent AuAgS/Ag2S nanoclusters show tunable luminescence depending on the nanocluster size. The apoptosis assay demonstrated that the AuAgS/Ag2S nanoclusters showed low cytotoxicity and good biocompatibility. Therefore, the nanoclusters can be used not only as a probe for labeling cells but also for their photocatalytic activity for photodegradation of organic dye. Moreover, a highly selective and sensitive assay for detection of mercury including Hg2+ and undissociated mercury complexes was developed based on the quenching fluorescent AuAgS/Ag2S nanoclusters, which provides a promising approach for determining various forms of Hg in the mercury-based compounds in environment. These unique nanoclusters may have potential applications in biological labeling, sensing mercury, and photodegradation of various organic pollutants in waste water.Graphical Abstract

Effects of surface wettability on gecko adhesion underwater

Recent experiments have shown that gecko adhesion underwater depends significantly on surface wettability. Theoretical models of a gecko seta adhering on different substrates are firstly established in order to disclose such an adhesion mechanism. The results show that the capillary force induced by nano-bubbles between gecko seta and the substrate is the mainly influencing factor. The capillary force exhibits an attractive feature between gecko setae and hydrophobic surfaces underwater. However, it is extremely weak or even repulsive on hydrophilic surfaces underwater. A self-similarly splitting model is further considered to simulate multiple gecko setae on substrates underwater. It is interesting to find that the total capillary force depends significantly on the number of nano-bubble bridges and wettability of substrates. The total force is attractive and increases monotonically with the increase of the splitting number on hydrophobic substrates underwater. However, it decreases drastically or even becomes repulsive on hydrophilic substrates underwater. The present result can not only give a reasonable explanation on the existing experimental observations but also be helpful for the design of novel biomimetic adhesives.

Successive detection of glucose and bio-copper in human serum based on a multiplex biosensor of gold nanorods

In this paper, a promising combined assay for the successive detection of blood glucose and sera copper levels based on etching of gold nanorods (GNRs) was developed. A hydroxyl radical-enhanced GNR oxidation under ultraviolet irradiation facilitates the establishment of a plasmonic biosensor that may quickly detect blood glucose. A linear relationship between the change of the plasmonic wavelength and the glucose concentration was found (Δλ = 4.2284 + 132.0c) in the range of 0.23 to 0.928 mM and the LOD was 0.45 μM. The determination of blood glucose using this proposed method was satisfactory and closely comparable to the results given by the local hospital. On the other hand, a blue-shift of the longitudinal plasmon wavelength induced by various forms of copper in the presence of Na2S2O3 provides a sensitive approach to detect the total copper level in a biological sample. The copper levels of human sera were measured and corroborated by flame atomic absorption spectrometry, which confirms that this approach might be applicable for bio-copper analysis with high accuracy. A combined assay for the successive detection of the blood glucose level and serum copper was subsequently developed. Compared to other related biosensors requiring a modified design, bio-molecular modification or/and sophisticated instruments, the dual glucose and copper sensor is very simple, cost-effective and easy to use for detection, suggesting great potential applications for successively monitoring blood glucose and copper concentrations and their changes during the progression of diabetes.

Versatile Sensitive Localized Surface Plasmon Resonance Sensor Based on Core-Shell Gold Nanorods for the Determination of Mercury(II) and Cysteine

A versatile sensitive localized surface plasmon resonance sensor was fabricated for the determination of mercury(II) and cysteine. The determination of mercury(II) was performed by taking advantage of the affinity between core-shell nanostructure and mercury to form a nanocomposite, leading to significant changes of localized surface plasmon resonance properties. The outstanding selectivity and sensitivity of the method provide a unique way to determine mercury(II) to concentrations as low as 5.00 × 10−8 M in aqueous solution. In addition, a strategy of orientation axially (end-to-end) assembly of core-shell gold nanorods at acidic medium was been developed that resulted in coupling of the plasmon band of core-shell gold nanorods, and was the basis of determining cysteine. An ultra-sensitive assay for the determination of cysteine was subsequently developed and levels of cysteine as low as 10−12 M can be determined. Compared with other gold nanorods-based sensors requiring molecular modification, these two approaches are simple in aqueous solution because of the unmodified design.

Alternate release of different target species based on the same gold nanorods and monitored by cell imaging.

In this study, a strategy for load and release of different kinds of molecules on the same gold nanorods (GNRs) was developed. An anticancer drug, doxorubicin hydrochloride (DOX), was firstly chemically conjugated on the GNRs. To efficiently load another type of target molecules DNA on the same GNRs, a polyelectrolyte Poly (ethylene imine) (PEI) was adsorbed on the GNR@DOX to form GNR@DOX@PEI. Then, the positive charge GNR@DOX@PEI allows the GNR conjugates to interact with negative charged DNA by an electrostatic interaction, enabling their full conjugation. A platform to load two kinds of target molecules conjugated on the same GNRs was fabricated. On the other hand, selective and sequential release of the different target species may be triggered by chemical reaction and near infrared (NIR) laser. The release of DOX was achieved by Na2S2O3 reacting with GNRs and the discharge of DNA conjugated on the GNR@DOX@PEI was accomplished by local-heating using NIR laser triggered release. Furthermore, the selective and alternate release of different target species from the GNRs inside MCF-7 cells was monitored by fluorescent imaging, providing a potential synergistic cancer treatment.