Changing the Blood Test: Accurate Determination of Mercury(II) in One Microliter of Blood Using Oriented ZnO Nanobelt Array Film Solution‐Gated Transistor Chips

The measurement of ultralow concentrations of heavy metal ions (HMIs) in blood is challenging. A new strategy for the determination of mercury ions (Hg²⁺) based on an oriented ZnO nanobelt (ZnO‐NB) film solution‐gated field‐effect transistor (FET) chip is adopted. The FET chips are fabricated with ZnO‐NB film channels with different orientations utilizing the Langmuir–Blodgett (L–B) assembly technique. The combined simulation and I–V behavior results show that the nanodevice with ZnO‐NBs parallel to the channel has exceptional performance. The sensing capability of the oriented ZnO‐NB film FET chips corresponds to an ultralow minimum detectable level (MDL) of 100 × 10^?12 m in deionized water due to the change in the electrical double layer (EDL) arising from the synergism of the field‐induced effect and the specific binding of Hg²⁺ to the thiol groups (‐SH) on the film surface. Moreover, the prepared FET chips present excellent selectivity toward Hg²⁺, excellent repeatability, and a rapid response time (less than 1 s) for various Hg²⁺ concentrations. The sensing performance corresponds to a low MDL of 10 × 10^?9 m in real samples of a drop of blood.     

Attomolar Electrochemical Detection of DNA Hybridization Based on Enhanced Latex/Gold Nanoparticles

We report a highly sensitive method for detecting DNA hybridization by anodic‐stripping voltammetry, using assemblies of AuNPs as electrochemical labels. The assemblies are made by layer‐by‐layer modification of sub‐micrometer latex spheres, followed by the uptake of the negatively charged AuNPs by ion exchange. The Au content can be considerably enhanced by autocatalytic reduction. Under the optimized conditions of enhancement, using differential pulse voltammetry for the stripping, 30 mer targets common to five strains of E. coli could be calibrated across the range 10 × 10^?18 M to 100 × 10^?18 M with a detection limit of 20 × 10^?18 M , which corresponds to ≈240 DNA hybridizations.     

Ultrasensitive SERS Substrate Integrated with Uniform Subnanometer Scale “Hot Spots” Created by a Graphene Spacer for the Detection of Mercury Ions

Mercuric ion (Hg²⁺) is one of the most toxic and serious environment polluting heavy metal ions, which can be accumulated in human body through food chains and drinking water, and causes serious damage to human organs. Therefore, development of the efficient and sensitive method for detection of Hg²⁺ is very necessary. In this study, the high surface sensitivity and fingerprint information about the chemical structures based on surface‐enhanced Raman scattering (SERS) for sensing applications are taken advantage of. Au triangular nanoarrays/n‐layer graphene/Au nanoparticles sandwich structure with large‐area uniform subnanometer gaps are fabricated and used to detect Hg²⁺ in water via thymine–Hg²⁺–thymine coordination; the detection limit of Hg²⁺ is as low as 8.3 × 10^?9m . Moreover, this SERS substrate is used to detect the Hg²⁺‐contaminated sandy soil and shows excellent performance. This study indicates the sandwich structure has a great potential in detection of toxic metal ions and environmental pollutants.     

TGF‐β1 Conjugated to Gold Nanoparticles Results in Protein Conformational Changes and Attenuates the Biological Function

Gold nanoparticles (AuNPs) are widely used as carriers or therapeutic agents due to their great biocompatibility and unique physical properties. Transforming growth factor‐beta 1 (TGF‐β1), a member of the cysteine‐knot structural superfamily, plays a pivotal role in many diseases and is known as an immunosuppressive agent that attenuates immune response resulting in tumor growth. The results reported herein reflect strong interactions between TGF‐β1 and the surface of AuNPs when incubated with serum‐containing medium, and demonstrate a time‐ and dose‐dependent pattern. Compared with other serum proteins that can also bind to the AuNP surface, AuNP–TGFβ1 conjugate is a thermodynamically favored compound. Epithelial cells undergo epithelial–mesenchymal transition (EMT) upon treatment with TGF‐β1; however, treatment with AuNPs reverses this effect, as detected by cell morphology and expression levels of EMT markers. TGF‐β1 is found to bind to AuNPs through S–Au bonds by X‐ray photoelectron spectroscopy. Fourier transform infrared spectroscopy is employed to analyze the conformational changes of TGF‐β1 on the surface of AuNPs. The results indicate that TGF‐β1 undergoes significant conformational changes at both secondary and tertiary structural levels after conjugation to the AuNP surface, which results in the deactivation of TGF‐β1 protein. An in vivo experiment also shows that addition of AuNPs attenuates the growth of TGF‐β1‐secreting murine bladder tumor 2 cells in syngeneic C3H/HeN mice, but not in immunocompromised NOD‐SCID mice, and this is associated with an increase in the number of tumor‐infiltrating CD4⁺ and CD8⁺ T lymphocytes and a decrease in the number of intrasplenic Foxp3(+) lymphocytes. The findings demonstrate that AuNPs may be a promising agent for modulating tumor immunity through inhibiting immunosuppressive TGF‐β1 signaling.     

Ultrasensitive Detection of Prostate‐Specific Antigen and Thrombin Based on Gold‐Upconversion Nanoparticle Assembled Pyramids

Self‐assembled nanostructures have been used for the detection of numerous cancer biomarkers. In this study, a gold‐upconversion‐nanoparticle (Au‐UCNP) pyramid based on aptamers is fabricated to simultaneously detect thrombin and prostate‐specific antigen (PSA) using surface‐enhanced Raman scattering (SERS) and fluorescence, respectively. The higher the concentration of thrombin, the lower the intensity of SERS. PSA connected with the PSA aptamer leads to an increase in fluorescence intensity. The limit of detection of thrombin and PSA reaches 57 × 10^?18 and 0.032 × 10^?18m , respectively. In addition, the pyramid also exhibits great target specificity. The results of human serum target detection demonstrate that the Au‐UCNP pyramid is an excellent choice for the quantitative determination of cancer biomarkers, and is feasible for the early diagnosis of cancer.     

Cytotoxicity of Ultrasmall Gold Nanoparticles on Planktonic and Biofilm Encapsulated Gram‐Positive Staphylococci

The emergence of multidrug resistant bacteria, especially biofilm‐associated Staphylococci, urgently requires novel antimicrobial agents. The antibacterial activity of ultrasmall gold nanoparticles (AuNPs) is tested against two gram positive: S. aureus and S. epidermidis and two gram negative: Escherichia coli and Pseudomonas aeruginosa strains. Ultrasmall AuNPs with core diameters of 0.8 and 1.4 nm and a triphenylphosphine‐monosulfonate shell (Au0.8MS and Au1.4MS) both have minimum inhibitory concentration (MIC) and minimum bactericidal concentration of 25 × 10^?6m [Au]. Disc agar diffusion test demonstrates greater bactericidal activity of the Au0.8MS nanoparticles over Au1.4MS. In contrast, thiol‐stabilized AuNPs with a diameter of 1.9 nm (AuroVist) cause no significant toxicity in any of the bacterial strains. Ultrasmall AuNPs cause a near 5 log bacterial growth reduction in the first 5 h of exposure, and incomplete recovery after 21 h. Bacteria show marked membrane blebbing and lysis in biofilm‐associated bacteria treated with ultrasmall AuNP. Importantly, a twofold MIC dosage of Au0.8MS and Au1.4MS each cause around 80%–90% reduction in the viability of Staphylococci enveloped in biofilms. Altogether, this study demonstrates potential therapeutic activity of ultrasmall AuNPs as an effective treatment option against staphylococcal infections.     

Electrical Graphene Aptasensor for Ultra‐Sensitive Detection of Anthrax Toxin with Amplified Signal Transduction

Detection of the anthrax toxin, the protective antigen (PA), at the attomolar (aM) level is demonstrated by an electrical aptamer sensor based on a chemically derived graphene field‐effect transistor (FET) platform. Higher affinity of the aptamer probes to PA in the aptamer‐immobilized FET enables significant improvements in the limit of detection (LOD), dynamic range, and sensitivity compared to the antibody‐immobilized FET. Transduction signal enhancement in the aptamer FET due to an increase in captured PA molecules results in a larger 30 mV/decade shift in the charge neutrality point (V_g,min) as a sensitivity parameter, with the dynamic range of the PA concentration between 12 aM (LOD) and 120 fM. An additional signal enhancement is obtained by the secondary aptamer‐conjugated gold nanoparticles (AuNPs‐aptamer), which have a sandwich structure of aptamer/PA/aptamer‐AuNPs, induce an increase in charge‐doping in the graphene channel, resulting in a reduction of the LOD to 1.2 aM with a three‐fold increase in the V_g,min shift.     

Split‐GFP: SERS Enhancers in Plasmonic Nanocluster Probes

The assembly of plasmonic metal nanoparticles into hot spot surface‐enhanced Raman scattering (SERS) nanocluster probes is a powerful, yet challenging approach for ultrasensitive biosensing. Scaffolding strategies based on self‐complementary peptides and proteins are of increasing interest for these assemblies, but the electronic and the photonic properties of such hybrid nanoclusters remain difficult to predict and optimize. Here, split‐green fluorescence protein (sGFP) fragments are used as molecular glue and the GFP chromophore is used as a Raman reporter to assemble a variety of gold nanoparticle (AuNP) clusters and explore their plasmonic properties by numerical modeling. It is shown that GFP seeding of plasmonic nanogaps in AuNP/GFP hybrid nanoclusters increases near‐field dipolar couplings between AuNPs and provides SERS enhancement factors above 10⁸. Among the different nanoclusters studied, AuNP/GFP chains allow near‐infrared SERS detection of the GFP chromophore imidazolinone/exocyclic C?C vibrational mode with theoretical enhancement factors of 10⁸–10⁹. For larger AuNP/GFP assemblies, the presence of non‐GFP seeded nanogaps between tightly packed nanoparticles reduces near‐field enhancements at Raman active hot spots, indicating that excessive clustering can decrease SERS amplifications. This study provides rationales to optimize the controlled assembly of hot spot SERS nanoprobes for remote biosensing using Raman reporters that act as molecular glue between plasmonic nanoparticles.     

DNA‐Driven Two‐Layer Core–Satellite Gold Nanostructures for Ultrasensitive MicroRNA Detection in Living Cells

It is a significant challenge to achieve controllable self‐assembly of superstructures for biological applications in living cells. Here, a two‐layer core–satellite assembly is driven by a Y‐DNA, which is designed with three nucleotide chains that hybridized through complementary sequences. The two‐layer core–satellite nanostructure (C₃₀S₅S₁₀ NS) is constructed using 30 nm gold nanoparticles (Au NPs) as the core, 5 nm Au NPs as the first satellite layer, and 10 nm Au NPs as the second satellite layer, resulting in a very strong circular dichroism (CD) and surface‐enhanced Raman scattering. After optimization, the yield is up to 85%, and produces a g‐factor of 0.16 × 10^?2. The hybridization of the target microRNA (miRNA) with the molecular probe causes a significant drop in the CD and Raman signals, and this phenomenon is used to detect the miRNA in living cells. The CD signal has a good linear range of 0.011–20.94 amol ng_RNA^?1 and a limit of detection (LOD) of 0.0051 amol ng_RNA^?1, while Raman signal with the range of 0.052–34.98 amol ng_RNA^?1 and an LOD of 2.81 × 10^?2 amol ng_RNA^?1. This innovative dual‐signal method can be used to quantify biomolecules in living cells, opening the way for ultrasensitive, highly accurate, and reliable diagnoses of clinical diseases.     

Enhancing sensitivity and selectivity of long-period grating sensors using structure-switching aptamers bound to gold-doped macroporous silica coatings

High surface area, sol-gel derived macroporous silica films doped with gold nanoparticles (AuNP) are used as a platform for high-density affinity-based immobilization of functional structure-switching DNA aptamer molecules onto Michelson interferometer long-period grating (LPG) fiber sensors, allowing for label-free detection of small molecular weight analytes such as adenosine triphosphate (ATP). The high surface area afforded by the sol-gel derived material allowed high loading of DNA aptamers, while the inclusion of gold nanoparticles within the silica film provided a high refractive index (RI) overlay, which is required to enhance the sensitivity of the LPG sensor according to our numerical simulations. By using a structure-switching aptamer construct that could release an oligonucleotide upon binding of ATP, the effective change in RI was both enhanced and inverted (i.e., binding of ATP caused a net reduction in molecular weight and refractive index), resulting in a system that prevented signals originating from nonspecific binding. This is the first report on the coupling of aptamers to LPG fiber sensors and the first use of high RI AuNP/silica films as supports to immobilize biomolecules onto the LPG sensor surface. The dual functionality of such films to both improve binding density and LPG sensor cladding refractive index results in a substantial enhancement in the sensitivity of such sensors for small molecule detection.     

Magnetic Bead/Gold Nanoparticle Double‐Labeled Primers for Electrochemical Detection of Isothermal Amplified Leishmania DNA

A novel methodology for the isothermal amplification of Leishmania DNA using labeled primers combined with the advantages of magnetic purification/preconcentration and the use of gold nanoparticle (AuNP) tags for the sensitive electrochemical detection of such amplified DNA is developed. Primers labeled with AuNPs and magnetic beads (MBs) are used for the first time for the isothermal amplification reaction, being the amplified product ready for the electrochemical detection. The electrocatalytic activity of the AuNP tags toward the hydrogen evolution reaction allows the rapid quantification of the DNA on screen‐printed carbon electrodes. Amplified products from the blood of dogs with Leishmania (positive samples) are discriminated from those of healthy dogs (blank samples). Quantitative studies demonstrate that the optimized method allows us to detect less than one parasite per microliter of blood (8 × 10^?3 parasites in the isothermal amplification reaction). This pioneering approach is much more sensitive than traditional methods based on real‐time polymerase chain reaction (PCR), and is also more rapid, cheap, and user‐friendly.     

Visualizing Human Telomerase Activity with Primer‐Modified Au Nanoparticles

Telomerase is over‐expressed in over 85% of all known human tumors. This renders the enzyme a valuable biomarker for cancer diagnosis and an important therapeutic target. The most widely used telomeric repeat amplification protocol (TRAP) assay has been questioned for telomerase detection. It is reported that human telomerase activity can be visualized by using primer‐modified Au nanoparticles. The working principle is based on the elongated primers conjugated to the gold nanoparticle (AuNP) surface, which can fold into a G‐quadruplex to protect the AuNPs from the aggregation. The developed simple and sensitive colorimetric assay can measure telomerase activity down to 1 HeLa cell µL^?1. More importantly, this assay can be easily extended to high‐throughput and automatic format. The AuNP‐TS method is PCR‐free and therefore avoids the amplification‐related errors and becomes more reliable to evaluate telomerase activity. This assay has also been used for initial screening of telomerase inhibitors as anticancer drug agents.     

Polyacrylonitrile-based electrospun nanofibers carrying gold nanoparticles in situ formed by photochemical assembly

Polyacrylonitrile (PAN) nanofibrous fabrics carrying gold nanoparticles (AuNPs) were prepared via the combination of electrospinning of PAN solution containing HAuCl₄ and in situ gold formation induced by ultraviolet (UV) irradiation. The factors to control the diameter of AuNPs were first investigated, and then their applicability to catalytic reaction using the obtained fibers was presented. The initial contents of Au ranging from 3 to 21 wt% did not exert a significant effect on the size of AuNPs formed in/on the PAN fibers, giving 4.7–5.4 nm in diameter, for 5 days of UV irradiation. On the other hand, the sizes of formed AuNPs were found to change from 5.2 to 2.7 nm with varying UV irradiation time from 5 to 1 day. The first-order rate constants obtained for the reduction of 4-nitrophenol increased from 1.1 × 10^?3, 3.5 × 10^?3 to 4.0 × 10^?3 s^?1, under a fixed volume of the fibers with AuNPs as catalysts, with increasing content of Au from 3, 13 to 21 wt%. The PAN catalysts with decreased size of AuNPs obtained through 1 day of UV irradiation gave a higher rate constant of 2.7 × 10^?2 s^?1. The highest rate constant per Au content and turnover frequency obtained in this study were 8.3 × 10^?2 s^?1 μmol-Au^?1 and 71 h^?1, respectively.     

Metal‐Ion‐Modified Black Phosphorus with Enhanced Stability and Transistor Performance

Black phosphorus (BP), a burgeoning elemental 2D semiconductor, has aroused increasing scientific and technological interest, especially as a channel material in field‐effect transistors (FETs). However, the intrinsic instability of BP causes practical concern and the transistor performance must also be improved. Here, the use of metal‐ion modification to enhance both the stability and transistor performance of BP sheets is described. Ag⁺ spontaneously adsorbed on the BP surface via cation–π interactions passivates the lone‐pair electrons of P thereby rendering BP more stable in air. Consequently, the Ag⁺‐modified BP FET shows greatly enhanced hole mobility from 796 to 1666 cm² V^?1 s^?1 and ON/OFF ratio from 5.9 × 10⁴ to 2.6 × 10⁶. The mechanisms pertaining to the enhanced stability and transistor performance are discussed and the strategy can be extended to other metal ions such as Fe³⁺, Mg²⁺, and Hg²⁺. Such stable and high‐performance BP transistors are crucial to electronic and optoelectronic devices. The stability and semiconducting properties of BP sheets can be enhanced tremendously by this novel strategy.     

A High‐Sensitivity and Low‐Power Theranostic Nanosystem for Cell SERS Imaging and Selectively Photothermal Therapy Using Anti‐EGFR‐Conjugated Reduced Graphene Oxide/Mesoporous Silica/AuNPs Nanosheets

A high‐sensitivity and low‐power theranostic nanosystem that combines with synergistic photothermal therapy and surface‐enhanced Raman scattering (SERS) mapping is constructed by mesoporous silica self‐assembly on the reduced graphene oxide (rGO) nanosheets with nanogap‐aligned gold nanoparticles (AuNPs) encapsulated and arranged inside the nanochannels of the mesoporous silica layer. Rhodamine 6G (R6G) as a Raman reporter is then encapsulated into the nanochannels and anti‐epidermal growth factor receptor (EGFR) is conjugated on the nanocomposite surface, defined as anti‐EGFR‐PEG‐rGO@CPSS‐Au‐R6G, where PEG is polyethylene glycol and CPSS is carbon porous silica nanosheets. SERS spectra results show that rGO@CPSS‐Au‐R6G enhances 5 × 10⁶ magnification of the Raman signals and thus can be applied in the noninvasive cell tracking. Furthermore, it displays high sensitivity (detection limits: 10^?8m R6G solution) due to the “hot spots” effects by the arrangements of AuNPs in the nanochannels of mesoporous silica. The highly selective targeting of overexpressing EGFR lung cancer cells (A549) is observed in the anti‐EGFR‐PEG‐rGO@CPSS‐Au‐R6G, in contrast to normal cells (MRC‐5). High photothermal therapy efficiency with a low power density (0.5 W cm^?2) of near‐infrared laser can be achieved because of the synergistic effect by conjugated AuNPs and rGO nanosheets. These results demonstrate that the anti‐EGFR‐PEG‐rGO@CPSS‐Au‐R6G is an excellent new theranostic nanosystem with cell targeting, cell tracking, and photothermal therapy capabilities.     

Amplification of Resonant Rayleigh Light Scattering Response Using Immunogold Colloids for Detection of Lysozyme

A strategy for attomolar‐level detection of small molecule‐size proteins is reported based on Rayleigh light scattering spectroscopy of individual nanoplasmonic aptasensors by exploiting the outstanding characteristics of gold colloids to amplify the nontransparent resonant signal at ultralow analyte concentrations. The fabrication method utilizes thiol‐mediated adsorption of a DNA aptamer on the immobilized Au nanoparticle surface, the interfacial binding characteristics of the aptamer with its target molecules, and the antibody–antigen interaction through plasmonic resonance coupling of the Au nanoparticles. Using lysozyme as a model analyte for disease detection, the detection limit of the aptasensor is ～7 × 10³ aM, corresponding to the LSPR λ_max shift of ～2.25 nm. Up to a 380% increase in the localized resonant λ_max shift is demonstrated upon antibody binding to the analyte compared to the primary response during signal amplification using immunogold colloids. This enhancement leads to a limit of detection of ～7 aM, which is an improvement of three orders of magnitude. The results demonstrate substantial promise for developing coupled plasmonic nanostructures for ultrasensitive detection of various biological and chemical analytes.     

Optical sensor based on 1,3-di(2-methoxyphenyl)triazene for monitoring trace amounts of mercury(II) in water samples

A new optical sensor for highly sensitive and selective determination of mercury(II) ion in aqueous solutions is developed. The mercury sensing membrane was prepared by incorporating 1,3-di(2-methoxyphenyl)triazene (MPT) as chromoionophore in the plasticized PVC membrane containing tris(2-ethylhexyl)phosphate (TEHP) as plasticizer. The proposed sensor displays a wide linear range of 9.0 × 10^?10–2.5 × 10^?7 M with a low detection limit of 2.0 × 10^?10 M in aqueous solutions at pH 4.0. This sensor has a relatively fast response time of less than 5 min. In addition to high stability and reproducibility, it shows a unique selectivity towards Hg²⁺ ion with respect to common coexisting cations. The sensor can readily be regenerated by exposure to a solution of sodium iodide (0.01 M). The proposed optode was applied to the determination of Hg²⁺ in water samples.     

The Role of Temperature and Lipid Charge on Intake/Uptake of Cationic Gold Nanoparticles into Lipid Bilayers

Understanding the molecular mechanisms governing nanoparticle–membrane interactions is of prime importance for drug delivery and biomedical applications. Neutron reflectometry (NR) experiments are combined with atomistic and coarse‐grained molecular dynamics (MD) simulations to study the interaction between cationic gold nanoparticles (AuNPs) and model lipid membranes composed of a mixture of zwitterionic di‐stearoyl‐phosphatidylcholine (DSPC) and anionic di‐stearoyl‐phosphatidylglycerol (DSPG). MD simulations show that the interaction between AuNPs and a pure DSPC lipid bilayer is modulated by a free energy barrier. This can be overcome by increasing temperature, which promotes an irreversible AuNP incorporation into the lipid bilayer. NR experiments confirm the encapsulation of the AuNPs within the lipid bilayer at temperatures around 55 °C. In contrast, the AuNP adsorption is weak and impaired by heating for a DSPC–DSPG (3:1) lipid bilayer. These results demonstrate that both the lipid charge and the temperature play pivotal roles in AuNP–membrane interactions. Furthermore, NR experiments indicate that the (negative) DSPG lipids are associated with lipid extraction upon AuNP adsorption, which is confirmed by coarse‐grained MD simulations as a lipid‐crawling effect driving further AuNP aggregation. Overall, the obtained detailed molecular view of the interaction mechanisms sheds light on AuNP incorporation and membrane destabilization.     

Quantifying the Nanomachinery of the Nanoparticle–Biomolecule Interface

A study is presented of the nanomechanical phenomena experienced by nanoparticle‐conjugated biomolecules. A thermodynamic framework is developed to describe the binding of thrombin‐binding aptamer (TBA) to thrombin when the TBA is conjugated to nanorods. Binding results in nanorod aggregation (viz. directed self‐assembly), which is detectable by absorption spectroscopy. The analysis introduces the energy of aggregation, separating it into TBA–thrombin recognition and surface‐work contributions. Consequently, it is demonstrated that self‐assembly is driven by the interplay of surface work and thrombin‐TBA recognition. It is shown that the work at the surface is about ?10 kJ mol^?1 and results from the accumulation of in‐plane molecular forces of pN magnitude and with a lifetime of <1 s, which arises from TBA nanoscale rearrangements fuelled by thrombin‐directed nanorod aggregation. The obtained surface work can map aggregation regimes as a function of different nanoparticle surface conditions. Also, the thermodynamic treatment can be used to obtain quantitative information on surface effects impacting biomolecules on nanoparticle surfaces.