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A ratio luminescence probe was developed for detecting Staphylococcus aureus (S. aureus) based on luminescence energy transfer (LET) using double‐wavelength emission (550 nm and 812 nm) upconversion nanoparticles (UCNPs) as donor, gold nanoparticles (AuNPs) as acceptor and the aptamer for S. aureus as the specific recognition and link unit. The LET process could cause luminescence quenching because of the spectral overlap between the acceptor and the donor at 550 nm. In the presence of S. aureus, S. aureus selectively combined with the aptamer, and the AuNPs left the surface of UCNPs, which weakened the quenching effect and restored the luminescence of UCNPs. Based on this, the ratio detection was realized by monitoring the change of the luminescence signal of the probe at 550 nm and taking the luminescence signal at 812 nm as the reference signal. Crucially, the probe has a fast reaction speed, with a reaction time of 25 min, and the detection of S. aureus is realized in the concentration range of 5.0 × 103–3.0 × 105 CFU/ml, with the detection limit of 106 CFU/ml. Therefore, the ratio probe has great potential for detecting of S. aureus in food because of its high sensitivity, fast speed and good selectivity. [ABSTRACT FROM AUTHOR]

An electrochemiluminescence resonance energy transfer (ECL-RET) system that detects prostate-specific antigen (PSA) was created. Near-infrared (NIR)-emitting NaYF:Yb,Tm/Mn upconverting nanoparticles (UCNPs) are used as donors, and gold nanorods (GNRs) are used as acceptors. The ECL was enhanced nearly threefold by Mn doping, with an emission peak appearing at an NIR wavelength of 808 nm. Anti-PSA 1 (Ab) was bound to the surfaces of UCNPs after being modified with poly(acrylic acid) (PAA). As for acceptors, cetyltrimethylammonium bromide (CTAB)-capped GNRs were treated with 11-mercaptoundecanoic acid (MUDA) and then conjugated with Anti-PSA 2 (Ab). When PSA was added, donors and acceptors were brought in close proximity through specific interactions of antibodies and antigens, resulting in high quenching efficiency levels. Under optimal conditions, the linear range of detection was 3.75-938 pg/mL for PSA ( R = 0.999), with a detection limit as low as 3.16 pg/mL. This method can be applied to detect PSA in human serums with satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemiluminescent DNA (ECL-DNA) sensor based on nano-gold signal enhancement (i.e. gold nanoparticles, GNP) and ferrocene signal quenching was investigated. The Au electrode was first modified with GNPs through electrodeposition method, followed by subsequent immobilization of single-stranded probe DNA labeled with ruthenium complex. The resulting sensor produced a higher ECL signal due to its higher density of self-assembled probe DNAs on the surface. Upon the hybridization of probe DNA with complementary target DNA labeled with ferrocene, ECL intensity decreased significantly due to spatial separation of ECL label from the electrode surface. As a result, the ECL signal was simultaneously quenched by ferrocene. The effects of both nano-gold electrodeposition time and ferrocene on the performance of ECL-DNA sensor were studied in detail and possible reasons for these effects were suggested as well. The reported ECL-DNA sensor showed great sensitivity and may provide an alternative approach for DNA detection in diagnostics and gene analysis. [Copyright &y& Elsevier]

Electrochemiluminescence (ECL) is a powerful readout method for the development of (bio)sensors, whose performances depend on the electrode materials and the architecture of its surface. Herein, we demonstrate that the precise control of the sensing interface using the versatility of two-dimensional (2D) transition metal carbides (Ti 3 C 2 T X MXene) leads to the enhancement of the ECL signal. This electrode material, which exhibits remarkable structural and electrochemical properties was decorated by the in situ formation of gold nanoparticles (AuNPs) owing to the Ti reducibility. Then, a large amount of the luminophore, Ru(bpy) 3 2+, was immobilized on Ti 3 C 2 T X MXene thanks to its unique negative charge and large specific surface area to obtain Ru–Ti 3 C 2 T X -AuNPs. The presented approach exploits the high catalytic activity and excellent conductivity of this 2D nanomaterial as illustrated by the enhanced ECL emission performance of the Ru–Ti 3 C 2 T X -AuNPs nanoprobes. Finally, DNA phosphorylated with polynucleotide kinase (PNK) was recognized efficiently by the chelation between Ti and phosphate group. A highly sensitive and selective ECL biosensor was developed for the detection of PNK and the screening of its inhibitors. A lower detection limit of 0.0002 U mL−1 and wide linear relationship ranged from 0.002 to 10 U mL−1 were obtained. Furthermore, the practicality of our method was tested in MCF-7 cell lysate, which opens enticing perspectives for future applications of Ti 3 C 2 T X materials in the ECL bioanalysis field. A precise control of the sensing interface using the versatility of two-dimensional (2D) transition metal carbides and nitrides (Ti 3 C 2 Tx MXene) leads to the enhancement of the ECL signal. In situ generation of AuNPs were decorated on Ti 3 C 2 Tx (Ti 3 C 2 Tx-AuNPs) owing to the Ti reducibility. Then, a large amount of the luminophore, Ru(bpy) 3 2+, was immobilized on Ti 3 C 2 Tx MXene thanks to its unique negative charge and large specific surface area to obtain Ru–Ti 3 C 2 Tx-AuNPs. Meanwhile, the DNA phosphorylated with PNK can be recognized efficiently by the chelation between Ti and phosphate group. [Display omitted] • In situ formation of Ti 3 C 2 Tx-AuNPs provide electrocatalytic rooting in Ti and Au. • Ru(bpy) 3 2+ was immobilized on the Ti 3 C 2 Tx-AuNPs to obtain probe of Ru– Ti 3 C 2 Tx -AuNPs. • DNA phosphorylated with PNK can be recognized by the chelation between Ti and PO 4 3-. • A sensitive and selective ECL biosensor was constructed for the detection of PNK. [ABSTRACT FROM AUTHOR]

Abstract: Based on the enhancement of chemiluminescence (CL) of luminol-hydrogen peroxide-gold nanoparticles system by fluoroquinolones (FQs), a novel and rapid CL method is reported for the determination of FQs derivatives. Under the optimum conditions, the CL intensity is proportional to the concentration of FQs derivative in solution. The corresponding linear regression equations are established over the range of 0.08–1.28μg/mL for norfloxacin, 0.013–1.32μg/mL for ciprofloxacin, 0.014–1.4μg/mL for lomefloxacin, 0.029–1.46μg/mL for fleroxacin, 0.02–1.0μg/mL for ofloxacin and 0.01–1.44μg/mL for levofloxacin, respectively. The limits of detection (S/N =3) are 3.2, 9.5, 7.0, 9.0, 8.0, and 8.0ng/mL with the relative standard deviation (n =11) 4.3, 1.5, 1.9, 1.3, 1.6 and 2.1% for norfloxacin, ciprofloxacin, lomefloxacin, fleroxacin, ofloxacin and levofloxacin, respectively. This proposed method has been applied to detect FQs derivatives in human urine successfully. [Copyright &y& Elsevier]

A novel luminescence energy transfer (LET) probe for detection of tumor related microRNAs using NaGdF 4 :Yb,Er@NaYF 4 upconversion nanoparticles (UCNPs) as energy donors and gold nanoparticles (AuNPs) as energy acceptors was developed. Using the double modified complementary DNA sequences of microRNA155 (miRNA155) as a bridge, NaGdF 4 :Yb,Er@NaYF 4 UCNPs and AuNPs were conjugated to form NaGdF 4 :Yb,Er@NaYF 4 UCNPs-DNA-AuNPs nanocomplexes (UCNPs-DNA-AuNPs) probe. The energy transfer would occur when the distance between donor and acceptor gets closer. In the presence of target miRNA155, DNA-RNA heteroduplexes appeared as product, but the luminescence intensity was not changed obviously. In the existence of duplex-specific nuclease (DSN), DSN could hydrolyze the DNA strand of DNA-RNA heteroduplexes, the bridge linked NaGdF 4 :Yb,Er@NaYF 4 UCNPs and AuNPs was destroyed, which induced that the quenched luminescence intensity was recovered and RNA was released. The released miRNA155 could react with another UCNPs-DNA-AuNPs probe to form DNA-RNA heteroduplexes again. This cyclic reaction generates an amplification of luminescence signal for quantitative detection of miRNA155. Under the illumination of 980 nm laser, the concentration ranges from 0.1 nM to 15 nM and the detection of limits was 0.045 nM for detection of miRNA155. Moreover, the UCNPs-DNA-AuNPs probe was used in quantify miRNA155 in cell lysates with satisfactory results. A novel luminescence energy transfer probe for detection of tumor related microRNAs using NaGdF 4 :Yb,Er@NaYF 4 upconversion nanoparticles (UCNPs) as energy donors and gold nanoparticles (AuNPs) as energy acceptors was developed. Using the double modified complementary DNA sequences of microRNA155 as a bridge, NaGdF 4 :Yb,Er@NaYF 4 UCNPs and AuNPs were conjugated to form UCNPs-DNA-AuNPs probe. The method has low background luminescence intensity, and amplificated signal induced by the cyclic of duplex-specific nuclease assisted. Moreover, the UCNPs-DNA-AuNPs probe was used in quantify microRNA155 in cell lysates with satisfactory results. Unlabelled Image • A LET probe was developed for determination of microRNA155. • The complementary DNA was used as a bridge to form UCNPs-DNA-AuNPs probe. • NaGdF 4 :Yb,Er@NaYF 4 UCNPs were used as the donor. • Gold nanoparticles were used as the acceptor. • Duplex specific nuclease was used to amplificate the determination signal. [ABSTRACT FROM AUTHOR]

A highly sensitive luminescent bioassay for the detection of Salmonella typhimurium was fabricated using Mn 2 + -doped NaYF 4 :Yb,Tm upconversion nanoparticles (UCNPs) as the donor and gold nanorods (Au NRs) as the acceptor and utilizing an energy transfer (LET) system. Mn 2 + -doped NaYF 4 :Yb,Tm UCNPs with a strong emission peak at 807 nm were obtained by changing the doped ion ratio. Carboxyl-terminated Mn 2 + -doped NaYF 4 :Yb,Tm UCNPs were coupled with S. typhimurium aptamers, which were employed to capture and concentrate S. typhimurium . The electrostatic interactions shorten the distance between the negatively charged donor and the positively charged acceptor, which results in luminescence quenching. The added S. typhimurium leads to the restoration of luminescence due to the formation of UCNPs-aptamers- S. typhimurium , which repels the UCNPs-aptamers from the Au NRs. The LET system does not occur because of the nonexistence of the luminescence emission band of Mn 2 + -doped NaYF 4 :Yb,Tm UCNPs, which had large spectral overlap with the absorption band of Au NRs. Under optimal conditions, the linear range of detecting S. typhimurium was 12 to 5 × 10 5 cfu/mL (R = 0.99). The limit of detection for S. typhimurium was as low as 11 cfu/mL in an aqueous buffer. The measurement of S. typhimurium in milk samples was satisfied in accordance with the plate-counting method, suggesting that the proposed method was of practical value in the application of food security. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, ultrasensitive detection of Ag+ is demonstrated by a biocatalytic signal amplification system which is realized by only one DNA sequence based electrical contacted enzyme structure and the Au nanoparticles/Carbon nanodots (AuNPs/C-dots) composite immobilization platform. In the presence of Ag+, with the interaction of cytosine–Ag+–cytosine (C–Ag+–C), cytosine-rich DNA sequence labeled with methylene blue (MB) molecules near 5′ end and Glucose Oxidase (GOx) at 3′ end, has a self-hybridization and then forms a duplex-like structure which makes MB and GOx approach the AuNPs/C-dots modified electrode. MB units can then act as a relay that electrically contacts GOx with the AuNPs/C-dots modified electrode and activate the bioelectrocatalyzed oxidation of glucose to glucose acid. In consequence, based on the bioelectrocatalyzed signal amplification on the AuNPs/C-dots platform, Ag+ could be quantitatively detected in the range of 10−11–10−5 M with a low detection limit of 3pM. Also, there is an excellent selectivity against other interferential metal ions. The detection of Ag+ ions was realized by Ag+ self-induced conformational change of DNA scaffold which involved only one oligonucleotide showing its convenience and availability. [Copyright &y& Elsevier]

Abstract: In this work, we design a FRET system for sensitive and selective determination of thrombin in red region, in which NaYF4:Yb,Er upconversion nanoparticles (UCNPs) act as donor and gold nanorods (Au NRs) act as acceptor. NaYF4:Yb,Er UCNPs with a strong emission at 661nm were successfully synthesized by tuning the doped ions ratio. Carboxyl-functionalized NaYF4:Yb,Er UCNPs and Au NRs were then prepared and conjugated with the thrombin aptamers, respectively. The fluorescence emission band of NaYF4:Yb,Er UCNPs (λ max=661nm) highly overlaps with the absorption band of Au NRs(λ max=666nm), which benefits from the large tunability of the spectrum band of Au NRs. A FRET system was then formed when thrombin was added to the mixture of NaYF4:Yb,Er UCNPs and Au NRs, which were both modified thrombin aptamers. The fluorescence quenching efficiency of NaYF4:Yb,Er UCNPs was increased in a thrombin concentration-dependent manner, which built the principle of thrombin quantification. The linear range was 2.5–90nM in an aqueous buffer, and 3.75–112.5nM in spiked human serum samples for thrombin. It also demonstrates a high selectivity to other biological species due to the specific binding. The measurement of thrombin in human plasma is satisfying, suggesting that the FRET system is of practical value in a complex biological sample matrix in red region. [Copyright &y& Elsevier]

A simple, sensitive fluorescent method for detecting biological aminothiols has been developed based on the inner filter effect principle that utilizes CePO4:Tb3+ luminescent nanoparticles as the donor and gold nanoparticles (AuNPs) as the energy receptor. Stable, water-soluble and well-dispersible CePO4:Tb3+ nanoparticles with low photobleaching features were synthesized conveniently by a facile solvothermal method. At the same time, AuNPs with a high extinction coefficient are expected to be capable of functioning as powerful receptor. Based on the complementary overlap between the emission spectrum of CePO4:Tb3+ nanoparticles and the absorption spectrum of Au NPs, an inner filter effect system was constructed. In the presence of aminothiols (such as cysteine), AuNPs interacted with the aminothiols, thereby inducing the aggregation of AuNPs, which induced the fluorescence recovery. In the present work, we developed a turn-on fluorescent assay for the determination of biological aminothiols. Under the optimum conditions, the linear concentration ranges were 1.0×10−7–2.0×10−6 M for cysteine, 5.0×10−8–5.0×10−7 M for glutathione and 8.0×10−8–1.0×10−6 M for homocysteine, respectively. The method is successfully applied to the quantification of biological aminothiols in synthetic samples. [ABSTRACT FROM AUTHOR]

Abstract: Determination of nucleotide kinase activity is valuable due to its importance in regulating nucleic acid metabolism. Herein, we describe a strategy for simply and accurately determining nucleotide kinase activity by TiO2 nanotubes mediated signal transition and Au nanoparticles amplification. In this method, DNA containing 5′-hydroxyl group is self-assembled onto a gold electrode and used as a substrate for T4 polynucleotide kinase (PNK). By the specific immobilization affinity of TiO2 nanotubes with the phosphorylated DNA, TiO2 nanotubes were linked with phosphorylated substrate DNA on the electrode. And then Au nanoparticles modified 5′-phosphate DNA was conjugated with the TiO2 nanotubes and hybridized with methylene blue labeled signal DNA. Because gold nanoparticles have high loading of signal indicator methylene blue, the electrochemical signal is generated and amplified. It presents an excellent performance with wide linear range and low detection limit. Additionally, inhibition effects of some salts have also been investigated. The developed method is a potentially useful tool in researching the interactions between proteins and nucleic acids and provides a diversified platform for a kinase activity assay. [Copyright &y& Elsevier]

Abstract: Ultrathin platinum-coated gold (Pt@Au) nanoparticles with core@shell structure have been developed by under-potential deposition (UPD) redox replacement technique. A single UPD Cu replacement with Pt2+ produced a uniform Pt monolayer on the surface of gold nanoparticles, which are immobilized on glassy carbon electrode (GCE) surface based on electrostatic interaction. The ultrathin Pt@Au nanoparticles were confirmed by cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). Voltammetry and amperometric methodologies were used to evaluate the electrocatalytic activity of the Pt@Au nanoparticles modified electrode towards the reduction of hydrogen peroxide under the physiological condition. The present results show that ultrathin Pt coating greatly enhances the electrocatalytic activity towards the reduction of hydrogen peroxide, which can be utilized to fabricate the hydrogen peroxide sensor. Chronoamperometric experiments showed that at an applied potential of 0.08V (vs. Ag/AgCl), the current reduction of hydrogen peroxide was linear to its concentration in the range of 1–450μΜ, and the detection limit was found to be 0.18μM (signal-to-noise ratio, S/N=3). [Copyright &y& Elsevier]

Abstract: In the present work, sensitive and stable sandwiched electrochemical immunosensing strategies with graphene (Gr)/gold nanoparticles (GNP) composite as the immobilization platform and ferrocene (Fc) derivatives as labels were proposed. Under the optimal choice and the proposed immunosensing strategy, with 1,1′-ferrocenedicarboxylic acid label, the human IgG could be detected specifically with a low detection limit of 0.4ng/mL and a wide linear dynamic range from 1 to 300ng/mL. Meanwhile, the electrochemical behavior of three different ferrocene derivatives labels was studied. [Copyright &y& Elsevier]

Abstract: A gold nanoparticles/TiO2 composite modified Indium tin oxide (ITO) electrode has been constructed to study the electrochemical behaviour of catechol (CC) and hydroquinone (HQ) using cyclic voltammetry and differential pulse voltammetry (DPV). Increasing of separation of the oxidative peak potentials and peak current for CC and HQ in pH 6.0 phosphate buffer solution (PBS), make it suitable for selected determination of CC. After the optimization of the conditions, CC was determined by DPV and the linear range is from 1.0×10−7 to 5.0×10−4 molL−1 with a correlation coefficient of 0.999 and limit of detection as 5.0×10−8 molL−1. Interference and stability study showed a satisfactory result. The proposed method has been applied to determine catechol in tea samples, and comparing with the chromatography the results are satisfactory. [Copyright &y& Elsevier]

Abstract: In this work, an electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of α-fetoprotein (AFP) was fabricated using Ru(bpy)3 2+-encapsulated liposome as the label and electrodeposited gold nanoparticles (GNPs) as the immobilizing support. Great signal amplification was achieved since liposome could encapsulate large amount of reporter molecules and GNPs could provide large active surface. Under optimized conditions, with sandwich type format, a linear range of AFP from 0.005 to 0.2pg/mL and an extremely low detection limit of 0.001pg/mL was obtained, much lower than that in previous reports. The proposed ECL immnuosensor showed high sensitivity, specificity, and good stability, which may open a new door to ultrasensitive detection of proteins in clinical analysis. [Copyright &y& Elsevier]

Abstract: A promising electrochemical sensor was fabricated by electrodeposition of gold nanoparticles on poly(3-methylthiophene) (P3MT)-modified glassy carbon electrode (GCE), forming a nano-Au/P3MT composites-modified GCE (nano-Au/P3MT/GCE). Field emission scanning electron microscope (FE-SEM) and electrochemical techniques were used for the characterization of these composites. It was found that nano-Au/P3MT layer was very uniform, and formed a kind of nanoporous structure. Electrochemical experiments showed that this proposed nano-Au/P3MT composites-modified electrode exhibited excellent electrocatalytic properties for nitrite and iodate. Amperometry revealed that there existed a good linear relationship between peak current with the concentration in the range of 10–1000μM and the detection limit of 2.3μM for nitrite and in the range of 5–500μM and the detection limit of 1.4μM for iodate. The proposed method has been used as an amperometric detector for analysis of nitrite and iodate in iodized table salt and results were satisfactory. The nano-Au/P3MT composites-modified electrode had good storage stability, reproducibility and anti-interference ability for promising practical application. [Copyright &y& Elsevier]

Abstract: Dithiocarbamate and gold nanoparticles have been successfully assembled onto the surface of the gold electrode and a novel ultrastable chemical modified electrode (CME) was fabricated conveniently. The as-prepared CME was investigated by electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM) and quartz crystal microbalance (QCM), and its electrochemical behaviors for catalytic oxidation of dopamine (DA) was also observed by cyclic voltammetry (CV) and amperometric i–t curve. The results indicated that the novel surface has endowed the electrode with not only ultrastability but also the advantages of organic ligands and gold nanoparticles, which open up a new way to design high efficient and utility electrochemical sensors for biomolecule detection. [Copyright &y& Elsevier]

Abstract: A novel electrochemical sensor has been constructed by use of a glassy carbon electrode (GCE) coated with a gold nanoparticle/choline (GNP/Ch). Electrochemical impedance spectroscopy (EIS), field emission scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the properties of this modified electrode. It was demonstrated that choline was covalently bounded on the surface of glassy carbon electrode, and deposited gold nanoparticles with average size of about 100nm uniformly distributed on the surface of Ch. Moreover, the modified electrode exhibits strong electrochemical catalytic activity toward the oxidation of dopamine (DA), ascorbic acid (AA) and uric acid (UA) with obviously reduction of overpotentials. For the ternary mixture containing DA, AA and UA, these three compounds can be well separated from each other, allowing simultaneously determination of DA and UA under coexistence of AA. The proposed method can be applied to detect DA and UA in real samples with satisfactory results. [Copyright &y& Elsevier]