Zong-Hong Lin

Toward Large-Scale Energy Harvesting by a Nanoparticle-Enhanced Triboelectric Nanogenerator

This article describes a simple, cost-effective, and scalable approach to fabricate a triboelectric nanogenerator (NG) with ultrahigh electric output. Triggered by commonly available ambient mechanical energy such as human footfalls, a NG with size smaller than a human palm can generate maximum short-circuit current of 2 mA, delivering instantaneous power output of 1.2 W to external load. The power output corresponds to an area power density of 313 W/m(2) and a volume power density of 54,268 W/m(3) at an open-circuit voltage of ~1200 V. An energy conversion efficiency of 14.9% has been achieved. The power was capable of instantaneously lighting up as many as 600 multicolor commercial LED bulbs. The record high power output for the NG is attributed to optimized structure, proper materials selection and nanoscale surface modification. This work demonstrated the practicability of using NG to harvest large-scale mechanical energy, such as footsteps, rolling wheels, wind power, and ocean waves.

Detection of mercury(II) based on Hg2+–DNA complexes inducing the aggregation of gold nanoparticles

A DNA-Au NP probe for sensing Hg2+ using the formation of DNA-Hg2+ complexes through thymidine (T)-Hg2+ -T coordination to control the negative charge density of the DNA strands-thereby varying their structures-adsorbed onto Au NPs.

Human Skin Based Triboelectric Nanogenerators for Harvesting Biomechanical Energy and as Self- Powered Active Tactile Sensor System

We report human skin based triboelectric nanogenerators (TENG) that can either harvest biomechanical energy or be utilized as a self-powered tactile sensor system for touch pad technology. We constructed a TENG utilizing the contact/separation between an area of human skin and a polydimethylsiloxane (PDMS) film with a surface of micropyramid structures, which was attached to an ITO electrode that was grounded across a loading resistor. The fabricated TENG delivers an open-circuit voltage up to -1000 V, a short-circuit current density of 8 mA/m(2), and a power density of 500 mW/m(2) on a load of 100 MΩ, which can be used to directly drive tens of green light-emitting diodes. The working mechanism of the TENG is based on the charge transfer between the ITO electrode and ground via modulating the separation distance between the tribo-charged skin patch and PDMS film. Furthermore, the TENG has been used in designing an independently addressed matrix for tracking the location and pressure of human touch. The fabricated matrix has demonstrated its self-powered and high-resolution tactile sensing capabilities by recording the output voltage signals as a mapping figure, where the detection sensitivity of the pressure is about 0.29 ± 0.02 V/kPa and each pixel can have a size of 3 mm × 3 mm. The TENGs may have potential applications in human-machine interfacing, micro/nano-electromechanical systems, and touch pad technology.

Integrated Multilayered Triboelectric Nanogenerator for Harvesting Biomechanical Energy from Human Motions

We demonstrate a new flexible multilayered triboelectric nanogenerator (TENG) with extremely low cost, simple structure, small size (3.8 cm×3.8 cm×0.95 cm) and lightweight (7 g) by innovatively integrating five layers of units on a single flexible substrate. Owing to the unique structure and nanopore-based surface modification on the metal surface, the instantaneous short-circuit current (Isc) and the open-circuit voltage (Voc) could reach 0.66 mA and 215 V with an instantaneous maximum power density of 9.8 mW/cm2 and 10.24 mW/cm3. This is the first 3D integrated TENG for enhancing the output power. Triggered by press from normal walking, the TENG attached onto a shoe pad was able to instantaneously drive multiple commercial LED bulbs. With the flexible structure, the TENG can be further integrated into clothes or even attached onto human body without introducing sensible obstruction and discomfort to human motions. The novel design of TENG demonstrated here can be applied to potentially achieve self-powered portable electronics.

A Self-Powered Triboelectric Nanosensor for Mercury Ion Detection**

Mercury is a highly toxic metal that can pose serious dangers to the environment and human health. Therefore, monitoring the mercury concentration is an extremely important issue to prevent such a toxic metal from endangering human life. Hg ions are by far the most stable inorganic form of mercury, which are non-biodegradable and bioaccumulable. Even at a very low concentrations, they can still be fatal to human brain, heart, and kidney. Multiple approaches, such as atomic absorption/emission spectrometry and inductively coupled plasma mass spectrometry (ICP-MS), have been applied to detect the Hg ions in environmental and biological samples. Among these approaches, ICP-MS is the method that has the highest sensitivity and the widest linear range. However, sample preparation before measurement is rather complicated and time-consuming, and requires expensive instrumentation and the use of noble gas. Another drawback of this method is the difficulty in performing infield analysis. In consideration of the above disadvantages, researchers have instead developed a number of optical methods (colorimetric or fluorometric assays, and systems based on surface plasmon resonance or surfaceenhanced Raman scattering) and electrochemical sensors for the detection of Hg ions. Optical approaches are advantageous in high sensitivity and selectivity, and practicable for in-field analysis, yet they are involved with sophisticated chemistry in incorporating organic probes, such as crown ethers, porphyrins, specific proteins, DNA, and polymers, which substantially limits their application range. To overcome the limitations of these methods, the concept of self-powered nanosensors has recently been proposed and tested for its potential toward toxic pollutant detection. The working principle of self-powered nanosensors is based on combining/integrating nanogenerators with sensors. The nanogenerators harvest energy from the environment to power the sensors. Owing to its convenient monitoring mechanism, the self-powered nanosensors could be the most desirable and promising prototype for environmental protection/detection in the near future because no battery is needed to power the device. For the time being, the major challenge is how to develop a fully integrated, stand-alone and selfpowered nanosensor. The triboelectric effect is an old but well-known phenomenon in daily life. Recently, it has been utilized as an effective way to harvest mechanical energy. Contact between two materials with different triboelectric polarity yields surface charge transfer. The periodic contact and separation of the oppositely charged surfaces can create a dipole layer and a potential drop, which drives the flow of electrons through an external load in responding to the mechanical agitation. As for triboelectric nanogenerator (TENG), maximizing the charge generation on opposite sides can be achieved by selecting the materials with the largest difference in the ability to attract electrons and changing the surface morphology. For the plate-structured TENG, it needs more time and stronger applied force to ensure the contact and separation of the two oppositely charged material surfaces upon pressing and releasing are complete, especially under the electrostatic attraction between them. Adding spacers between two plates or using arch-shaped substrates have been demonstrated to improve the output of TENG. Herein, we show that the principle of the TENG can be used as a sensor for the detection of Hg ions. The first step is to improve the performance of the TENG through the assembly of Au nanoparticles (NPs) onto the metal plate. These assembled AuNPs not only act as steady gaps between the two plates at the strain-free condition, but also enable the function of enlarging the contact area of the two plates, which will increase the electrical output of the TENG. Through further modification of 3-mercaptopropionic acid (3-MPA) molecules on the assembled AuNPs, the high-output nanogenerator can become a highly sensitive and selective nanosensor toward Hg ions detection because of the different triboelectric polarity of AuNPs and Hg ions. On the basis of this unique structure, the output voltage and current of the triboelectric nanosensor (TENG) reached 105 V and 63 mA with an effective dimension of 1 cm 1 cm. Under optimum conditions, this TENG is selective for the detection of Hg ions, with a detection limit of 30 nm and linear range from 100 nm to 5 mm. A commercial LED lamp was tested as the indicator to replace the expensive electrometer and showed the possibility to simplify the detection system. Our study demonstrates an innovative and unique approach toward selfpowered detection of Hg. [*] Dr. Z.-H. Lin, G. Zhu, Y. S. Zhou, Dr. Y. Yang, P. Bai, J. Chen, Prof. Z. L. Wang School of Material Science and Engineering Georgia Institute of Technology, Atlanta, GA 30332-0245 (USA) E-mail: zlwang@gatech.edu

Synthesis of Fluorescent Carbohydrate-Protected Au Nanodots for Detection of Concanavalin A and Escherichia coli

This study describes a novel, simple, and convenient method for the preparation of water-soluble biofunctional Au nanodots (Au NDs) for the detection of Concanavalin A (Con A) and Escherichia coli (E. coli). First, 2.9 nm Au nanoparticles (Au NPs) were prepared through reduction of HAuCl(4).3H(2)O with tetrakis(hydroxymethyl)phosphonium chloride (THPC), which acts as both a reducing and capping agent. Addition of 11-mercapto-3,6,9-trioxaundecyl-alpha-D-mannopyranoside (Man-SH) onto the surfaces of the as-prepared Au NPs yielded the fluorescent mannose-protected Au nanodots (Man-Au NDs) with the size and quantum yield (QY) of 1.8 (+/-0.3) nm and 8.6%, respectively. This QY is higher than those of the best currently available water-soluble, alkanethiol-protected Au nanoclusters. Our fluorescent Man-Au NDs are easily purified and by multivalent interactions are capable of sensing, under optimal conditions, Con A with high sensitivity (LOD = 75 pM) and remarkable selectivity over other proteins and lectins. To the best of our knowledge, this approach provided the lowest LOD value for Con A when compared to the other nanomaterials-based detecting method. Furthermore, we have also developed a new method for fluorescence detection of E. coli using these water-soluble Man-Au NDs. Incubation with E. coli revealed that the Man-Au NDs bind to the bacteria, yielding brightly fluorescent cell clusters. The relationship between the fluorescence signal and the E. coli concentration was linear from 1.00 x 10(6) to 5.00 x 10(7) cells/mL (R(2) = 0.96), with the LOD of E. coli being 7.20 x 10(5) cells/mL.

Triboelectric Nanogenerator for Harvesting Wind Energy and as Self-Powered Wind Vector Sensor System

We report a triboelectric nanogenerator (TENG) that plays dual roles as a sustainable power source by harvesting wind energy and as a self-powered wind vector sensor system for wind speed and direction detection. By utilizing the wind-induced resonance vibration of a fluorinated ethylene-propylene film between two aluminum foils, the integrated TENGs with dimensions of 2.5 cm × 2.5 cm × 22 cm deliver an output voltage up to 100 V, an output current of 1.6 μA, and a corresponding output power of 0.16 mW under an external load of 100 MΩ, which can be used to directly light up tens of commercial light-emitting diodes. Furthermore, a self-powered wind vector sensor system has been developed based on the rationally designed TENGs, which is capable of detecting the wind direction and speed with a sensitivity of 0.09 μA/(m/s). This work greatly expands the applicability of TENGs as power sources for self-sustained electronics and also self-powered sensor systems for ambient wind detection.

Bioconjugated gold nanodots and nanoparticles for protein assays based on photoluminescence quenching.

This study describes the first instance of the use of two differently sized Au nanoparticles (Au NPs), acting separately as donor and acceptor, in homogeneous photoluminescence quenching assays developed for the analysis of proteins. Introduction of a breast cancer marker protein, platelet-derived growth factor AA (PDGF AA), to a solution of 11-mercaptoundecanoic acid-protected, 2.0-nm photoluminescent Au nanodots (L(AuND)) led to the preparation of PDGF AA-L(AuND) as the donor. Thiol-derivative PDGF binding aptamers (Apt) and 13-nm spherical Au NPs were used to synthesize the Apt-Q(AuNP) acceptor. The photoluminescence of PDGF AA-L(AuND) at 520 nm decreased when photoluminescence quenching occurred between Apt-Q(AuNP) and PDGF AA-L(AuND). We used the PDGF AA-L(AuND)/Apt-Q(AuNP)-based molecular light switching system to analyze PDGFs and PDGF alpha-receptor in separate homogeneous solutions. In the presence of PDGFs, the interaction between Apt-Q(AuNP) and PDGF AA-L(AuND) decreased as a result of competitive reactions between the PDGFs and Apt-Q(AuNP). Similarly, the interaction between Apt-Q(AuNP) and PDGF AA-L(AuND) reduced as a result of competitive reactions between PDGF alpha-receptor and PDGF AA-L(AuND). The limits of detection (LODs) for PDGF AA and PDGF alpha-receptor were 80 pM and 0.25 nM, respectively, resulting from a low background photoluminescence signal. When using the Apt-Q(AuNP) as selectors for (a) the enrichment of PDGF AA and (b) the removal of matrixes possessing intense background fluorescence from cell media and urine samples, the LOD for PDGF AA decreased to 10 pM. Unlike quantum dots, the L(AuND) provide the advantages of biocompatibility, ease of bioconjugation, and minimal toxicity.

Harvesting Water Drop Energy by a Sequential Contact‐Electrification and Electrostatic‐Induction Process

A new prototype triboelectric nanogenerator with superhydrophobic and self-cleaning features is invented to harvest water drop energy based on a sequential contact electrification and electrostatic induction process. Because of the easy-fabrication, cost-effectiveness, and robust properties, the developed triboelectric nanogenerator expands the potential applications to harvesting energy from household wastewater and raindrops.

Water–Solid Surface Contact Electrification and its Use for Harvesting Liquid‐Wave Energy

Contact electrification, also called triboelectrification, is an old but well-known phenomenon in which surface charge transfer occurs when two materials are brought into contact. Although some of the fundamental mechanisms about triboelectrification are still under discussion, such as what subjects (electrons, ions, or small amounts of material) are transferred during the contact and separation process to produce the charged surface, and why surface charge transfer occurs even between identical materials, triboelectrification does exist and it has some practical applications together with many negative consequences. Recently, contact electrification has been demonstrated for some potential applications, such as energy harvesting, chemical sensors, 6] electrostatic charge patterning, metal-ion reduction, and laser printing. The triboelectric nanogenerator (TENG), which is the first invention utilizing contact electrification to efficiently convert mechanical energy into electricity, has been systematically studied to instantaneously drive hundreds of lightemitting diodes (LEDs) and charge a lithium-ion battery for powering a wireless sensor and a commercial cell phone. Recently, the research has been broadened to collect energy from environment, such as wind and human motion, under which the TENG works in relatively dry conditions, because the surface triboelectrification would be greatly decreased if not totally eliminated by the presence of water. However, water vapor and liquid water are abundant and the most obvious example is ocean waves and tides that have huge amounts of mechanical energy, which is inexhaustible and not largely dictated by daytime, season, weather and climate, in contrast to solar energy. Until now, TENG is designed to work between solid materials and works best under dry conditions. 13–16] However, tribolelectricity does exist when liquids are flowing through insulating tubes. For example, a voltage variation rising up to 300 mV is observed when deionized water flows through a 1 m-long rubber tube. Or a surface charge density of 4.5 mC m 2 is measured on each water droplet pipetted from a polytetrafluoroethylene (PTFE) tip. Therefore, herein we explore the opportunity to use water contact as one type of “material” choice for TENG. We demonstrate that the contact electrification between water and insulating polymer films can also be useful for TENG, which can derive a new application of TENG especially in liquid environments for sensing. Polydimethylsiloxane (PDMS) and PTFE are chosen in this study for their hydrophobic properties and high negativity in the triboelectric series. To further investigate this effect, TENGs using tap water, deionized water, and deionized water with a high concentration of NaCl are also compared. Under periodic contacting deionized water by a linear motor, PDMS film with patterned pyramid array can provide an open-circuit voltage (Voc) of 52 V and short-circuit current density (Jsc) exceeding 2.45 mAm 2 with a peak power density of nearly 0.13 W m , which is large enough to light up 60 commercial LEDs. The incubation shaker and platform rocker are used to stimulate different wave motions in the environment and the water–TENG successfully harvests these types of mechanical energy into electricity. Moreover, the water–TENG also has the capability to act as a chemical and temperature sensor. Figure 1 shows the fabrication process of the TENG and how the water contact electrification is included in the action unit. The TENG fabrication starts from the design of a PDMS film with patterned pyramid array (Figure 1a). The Si wafer mold was made by photolithography and then etched by a dry etching process. Liquid PDMS elastomer and cross-linker were mixed, degassed, and uniformly spin-coated on the Si wafer mold. After thermal incubation, a uniform PDMS film with a patterned pyramid array was formed. For the other part of the construct, thin films of Cu (100 nm) were deposited on two poly(methyl methacrylate) (PMMA) substrates by a RF magnetron sputtering deposition system. PMMA is selected as the substrate material because it provides a flat surface, light weight, and high strength. The PDMS film with the pyramid array pattern was peeled off the Si wafer mold and then placed on one of the Cu thin-film-deposited PMMA substrates with uncured PDMS mixture on top. Finally, the structure was incubated again to obtain a fully developed device for use in the next step. To investigate the contact electrification between water and the PDMS film, the second Cu thin-film-deposited PMMA substrate was placed on the bottom of an insulating tank (Figure 1b), acting as the conducting electrode for the water. The dimensions of the tank were 11 cm 7 cm. After the tank was filled with water, the device consisting of the [*] Dr. Z.-H. Lin, Dr. G. Cheng, L. Lin, Dr. S. Lee, Prof. Z. L. Wang School of Material Science and Engineering Georgia Institute of Technology Atlanta, GA 30332-0245 (USA) E-mail: zlwang@gatech.edu