FehlererKennung und Programmoptimierung in der ET-AAS durch zeitaufgel?ste Signale (Direkte Elementspurenbestimmung in Harn: Cd, Co, Cr, Ni, Tl, Pb)

Summary The direct determination of trace elements in urines with ET-AA-spectrometry leads to numerous systematic errors. Part of these errors can be discovered by time-resolved signals and can thereby be avoided. Contrary to the assumption that optimal results can be obtained via the signal area, it is often the measurement of the signal height, which is to be given preference (better ratio of atomic absorption signal/background signal). Phosphate-containing matrix modifiers cause systematic interferences; their use should therefore be avoided. The determination of cobalt traces with the ET-AA-spectrometry and with D₂-background correction will always yield wrong values, if samples contain at the same time phosphorous oxygen compounds as well as alkali compounds. Previous Co-determinations which were carried out with this method, should therefore be controlled in a number of biotic matrices. When Zeeman-correction is used, such errors will not occur.     

Sensitive fluorescent detection of Staphylococcus aureus using nanogold linked CdTe nanocrystals as signal amplification labels

A sensitive fluorescent assay was developed for the detection of DNA specifically for Staphylococcus aureus. A sandwich-type detection system was fabricated by first immobilizing biotinylated capture DNA on avidin-modified wells of microplates, then hybridizing the capture DNA with one end of the target DNA, and then recognizing the other end of the target DNA with a signal probe labeled with CdTe nanocrystals and gold nanoparticles (Au-NPs) at the 3′- and 5′-terminus, respectively. Hybridization was monitored by measuring the fluorescent intensity of the assembly. The experimental results demonstrated that the incorporation of Au-NPs in this detection system can significantly enhance the sensitivity and the selectivity because a single Au-NP can be loaded with hundreds of signal DNA probe strands modified with CdTe nanocrystals. Under the optimized conditions, a detection limit of 10 fmol of DNA per L can be achieved and at least 50 colony forming units of Staph. aureus per mL of sample can be detected. The method was assessed by analyzing real samples, and it was validated by comparing it to an official standard method.

Thermosensitive and Dissolution Properties in Nanocomposite Polymer Hydrogels

We investigate the phase transition behavior and dissolution resistant properties of thermo‐sensitive nanocomposite hydrogels made from PEO‐PPO‐PEO triblock copolymer (Pluronic F127) and Laponite silicate nanoparticles. The rapid dissolution properties of F127 copolymer hydrogels usually limit their use as sustained release drug carriers. We overcome this limitation by synergistic combination of nanoparticle gelation characteristics with polymer thermo‐sensitivity. We present a proof of concept that the temperature‐dependent phase transitions can be shifted as a function of hydrogel composition and that the dissolution of the polymer hydrogels as well as the release of a model drug, albumin, can be significantly slowed down by addition of nanoparticles. The dissolution resistant properties generated will prove useful in the future formulation, processing and application of our polymer hydrogels for sustained release drug delivery carriers.

     

Lithiumbestimmung mit Matrixmodifier KH2PO4 in Triton X-100 im biologischen Material

Summary The measurement signal of lithium is especially strongly suppressed in biological material by sodium, calcium and magnesium. The method described largely prevents this signal lowering by treatment of the sample with KH₂PO₄ in the determination of lithium with electrothermal atomic absorption. This makes a further processing of the serum sample by digestion superfluous. Calibration is carried out with the standard addition procedure. With the method presented, a limit of detection of 0.5 g lithium/l serum can be attained with an injection volume of 20 l.     

A sodium-selective optrode

An ion selective optrode (ISO) for continuous determination of sodium is presented. It is based on the optical measurement of the membrane potential between an aqueous sample solution and a lipid membrane phase with the help of a potential-sensitive dye. The lipid membrane is composed of rhodamine B C-18 ester together with the sodium selective ionophore ETH 157 and either arachidic acid or 1-octadecanol, and is prepared by using the Langmuir-Blodgett (LB) technique. The fluorescence intensity of the dye reversibly responds to the sodium ion concentration. Fluorescence decreases with increasing sodium concentraction. Interferences by potassium or calcium can be compensated for by using a reference optrode. The sodium sensor works in the 1 to 100 mM sodium ion concentration range with a maximal signal change of –4.2% of the full scale signal for 100 mM. The relationship between the relative signal change (I/I) and the negative logarithm of the sodium concentration is linear over two orders of magnitude. The selectivity coefficients over potassium or calcium are better than 1 × 10⁵ when use is made of a reference optrode. The sensors can be stored under air for more than half a year without loss in fluorescence intensity or changes in response function.     

Anthraquinonyl glycoside facilitates the standardization of graphene electrodes for the impedance detection of lectins

Background

Construction of electrochemical impedance sensors by the self-assembly technique has become a promising strategy for the `label-free' detection of protein-ligand interactions. However, previous impedance sensors are devoid of an inherent electrochemical signal, which limits the standardization of the sensors for protein recognition in a reproducible manner.

Results

We designed and synthesized an anthraquinonyl glycoside (AG) where the anthraquinone (AQ) moiety can bind to the surface of a graphene-based working electrode while the glycoside serving as a ligand for lectin. By measuring the inherent voltammetric signal of AQ, the glycosides decorated on the working electrode could be simply quantified to obtain electrodes with a unified signal window. Subsequently, impedance analysis showed that the `standardized' electrodes gave a reproducible electrochemical response to a selective lectin with no signal variation in the presence of unselective proteins.

Conclusion

Anthraquinone-modified ligands could be used to facilitate the standardization of electrochemical impedance sensors for the reproducible, selective analysis of ligand-protein interactions.

     

Quantum dots on electrodes—new tools for bioelectroanalysis

The review covers recent developments in which quantum dots (QDs) are combined with electrodes for detection of analytes. Special focus will be on the generation of photocurrents and the possibility of spatially resolved, light-directed analysis. Different modes for combining biochemical reactions with QDs will be discussed. Other applications involve the use of QDs as labels in binding analysis. Different methods have been developed for read-out. In addition to photocurrent analysis, voltammetric detection of metals and electrochemiluminescence (ECL) can be used. In the latter, light is the sensor signal. ECL-based systems combine the advantage of very sensitive analytical detection with rather simple instrumentation.

Integration of exonuclease III-powered three-dimensional DNA walker with single-molecule detection for multiple initiator caspases assay

Initiator caspases are important components of cellular apoptotic signaling and they can activate effector caspases in extrinsic and intrinsic apoptotic pathways. The simultaneous detection of multiple initiator caspases is essential for apoptosis mechanism studies and disease therapy. Herein, we develop a sensitive nanosensor based on the integration of exonuclease III (Exo III)-powered three-dimensional (3D) DNA walker with single-molecule detection for the simultaneous measurement of initiator caspase-8 and caspase-9. This assay involves two peptide–DNA detection probe-conjugated magnetic beads and two signal probe-conjugated gold nanoparticles (signal probes@AuNPs). The presence of caspase-8 and caspase-9 can induce the cleavage of peptides in two peptide–DNA detection probes, releasing two trigger DNAs from the magnetic beads, respectively. The two trigger DNAs can serve as the walker DNA to walk on the surface of the signal probes@AuNPs powered by Exo III digestion, liberating numerous Cy5 and Texas Red fluorophores which can be quantified by single-molecule detection, with Cy5 indicating caspase-8 and Texas Red indicating caspase-9. Notably, the introduction of the AuNP-based 3D DNA walker greatly reduces the background signal and amplifies the output signals, and the introduction of single-molecule detection further improves the detection sensitivity. This nanosensor is very sensitive with a detection limit of 2.08 × 10⁻⁶ U μL⁻¹ for caspase-8 and 1.71 × 10⁻⁶ U μL⁻¹ for caspase-9, and it can be used for the simultaneous screening of caspase inhibitors and the measurement of endogenous caspase activity in various cell lines at the single-cell level. Moreover, this nanosensor can be extended to detect various proteases by simply changing the peptide sequences of the detection probes.

We demonstrate the simultaneous detection of multiple initiator caspases by integrating exonuclease III-powered three-dimensional DNA walker with single-molecule detection.     

A sensitive chemiluminescence method for the determination of cysteine based on silver nanoclusters

We have developed a sensitive chemiluminescent (CL) assay for cysteine. It is based on the use of water-soluble and fluorescent silver nanoclusters (Ag NCs) which are found to be able to strongly enhance the weak CL signal resulting from the redox reaction between Ce(IV) ion and sulfite ion. This enhancement is inhibited by cysteine under appropriate conditions. Taking advantage of this specific CL inhibition, a novel CL method for the sensitive and selective detection of cysteine was developed. This effect is interpreted in terms of an electronic energy transfer from excited state intermediate sulfur dioxide (originating from the CL reaction between Ce(IV) and sulfite ions) to the Ag-NCs. The latter become electronically excited and thus can act as a new source of emission. The method was applied to the determination of cysteine in the range from 5.0?nM to 1.0?μM, with a detection limit at 2.5?nM (S/N?=?3).

Aptamer based fluorescent cocaine assay based on the use of graphene oxide and exonuclease III-assisted signal amplification

The article reports an aptamer based assay for cocaine by employing graphene oxide and exonuclease III-assisted signal amplification. It is based on the following scheme and experimental steps: (1) Exo III can digest dsDNA with blunt or recessed 3-terminus, but it has limited activity to ssDNA or dsDNA with protruding 3-terminus; (2) GO can absorb the FAM-labeled ssDNA probe and quench the fluorescence of probe, while the affinity between FAM-labeled mononucleotide and GO is negligible; (3) Cocaine aptamer can be split into two flexible ssDNA pieces (Probe 1 and Probe 2) without significant perturbation of cocaine-binding abilities; (4) The triple complex consisting of Probe 1, Probe 2 and cocaine can be digested by Exo III with the similar efficiency as normal dsDNA. Cocaine aptamer is split into two flexible ssDNA pieces (Probe 2 and 3′-FAM-labeled Probe 1). Cocaine can mediate the cocaine aptamer fragments forming a triplex. The triple complex has unique characteristic with 3′-FAM-labeled blunt end at the Probe 1 and 3′-overhang end at Probe 2. If exonuclease III is added, it will catalyze the stepwise removal of fluorescein (FAM) labeled mononucleotides from the 3-hydroxy termini of the special triplex complex, resulting in liberation of cocaine. The cocaine released in this step can produce a new cleavage cycle, thereby leading to target recycling. Through such a cyclic bound-hydrolysis process, small amounts of cocaine can induce the cleavage of a large number of FAM-labeled probe 1. The cleaved FAM-labeled mononucleotides are not adsorbed on the surface of graphene oxide (GO), so a strong fluorescence signal enhancement is observed as the cocaine triggers enzymatic digestion. Under optimized conditions, the assay allows cocaine to be detected in the 1 to 500 nM concentration range with a detection limit of 0.1 nM. The method was applied to the determination of cocaine in spiked human plasma, with recoveries ranging from 92.0 to 111.8 % and RSD of <12.8 %.

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Graphical abstract Aptamer based fluorescent cocaine assay based on graphene oxide and exonuclease III-assisted signal amplification

     

One step synthesis,characterization of F127-Mn+-chlorpyrifos mesoporous silica for sustained release system with pH sensitivity

The triblock copolymer F127 (molecular formula (EO)₁₀₆(PO)₇₀(EO)₁₀₆) was adopted as template with TMOS as the silica source. They were hydrolyzed by acidic aqueous solution in which chlorpyrifos (CH) and metal ions (Mⁿ⁺) were introduced to the products to construct "F127-Mⁿ⁺-CH" coordination structure in one step. Different sustained release systems were prepared through changing the composition of acidic aqueous solution added during the preparation. The characterization results confirmed the coordination interaction existing among metal ions, mesoporous silica and chlorpyrifos. It was also proved that the chlorpyrifos loaded in the sustained release system existed as amorphous state. According to SEM and TEM observation, the pore of the material presented as face-centered cage-type cubic structure with IM-3M symmetry similar to SBA-16 which is in accordance with N₂ adsorption isotherms. The as-synthesized system showed significant pH sensitivity in the sustained release process indicating that the sustained release system can be well stored in neutral environment and activated while sprayed into earth in acid or basic environment. Their sustained release curves can be described by Korsmeyer-Peppas equation in neutral while accords with Higuchi under acid or basic environment.     

Signal limitations in tip-enhanced Raman scattering: the challenge to become a routine analytical technique

The fundamental parameters and limitations that determine the signal strength in tip-enhanced Raman scattering (TERS) are discussed. A semiquantitative analysis of the Raman signal expected in different experimental geometries and with different sample systems is presented, taking into account experimental parameters including Fresnel factor, numerical aperture of the illumination and collection optics, detection efficiency, and the Raman scattering cross section of the material. A top/side-on illumination geometry is essential for the study of nontransparent samples. It can yield the highest signal levels when strong tip–sample coupling using a metallic substrate provides large field enhancement. In contrast, axial/through-sample illumination is limited to transparent sample materials. Although conceptually simpler in experimental implementation and despite high numerical aperture signal collection efficiency, signals are generally weaker due to limited field enhancement. Crystalline solids with small Raman cross sections and dense molecular/biological systems with unavoidable far-field background provide the biggest challenge for TERS analysis yet at the same time hold the most exciting outstanding scientific questions TERS has the potential to answer.

A metal-organic framework sustained by a nanosized Ag12 cuboctahedral node for solid-phase extraction of ultra traces of lead(II) ions

We show that a metal-organic framework (MOF) sustained by a nanosized Ag12 cuboctahedral node can be applied to selectively extract traces of lead(II) ion from environmental water samples. The MOF was characterized by thermogravimetric and differential thermal analysis, scanning electron microscopy, FTIR, and X-ray diffraction. The effects of pH value, flow rates, of type, concentration and volume of the eluent, of break-through volume and potentially interfering ions on the separation and determination of lead were evaluated. Following desorption with EDTA, Pb(II) was quantified by FAAS. The use of the MOF results in excellent analytical figures of merit including an analytical range from 2 to 180 μg L^?1 of Pb(II) (R²?>?0.99); a limit of detection of 500 ng L^?1; an adsorption capacity of 120 mg g^?1; an extraction efficiency of >95 %, and a relative standard deviation of <4 % (for eight separate column experiments).

Characterization of Harmonic Signal Acquisition with Parallel Dipole and Multipole Detectors

Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is a powerful instrument for the study of complex biological samples due to its high resolution and mass measurement accuracy. However, the relatively long signal acquisition periods needed to achieve high resolution can serve to limit applications of FTICR-MS. The use of multiple pairs of detector electrodes enables detection of harmonic frequencies present at integer multiples of the fundamental cyclotron frequency, and the obtained resolving power for a given acquisition period increases linearly with the order of harmonic signal. However, harmonic signal detection also increases spectral complexity and presents challenges for interpretation. In the present work, ICR cells with independent dipole and harmonic detection electrodes and preamplifiers are demonstrated. A benefit of this approach is the ability to independently acquire fundamental and multiple harmonic signals in parallel using the same ions under identical conditions, enabling direct comparison of achieved performance as parameters are varied. Spectra from harmonic signals showed generally higher resolving power than spectra acquired with fundamental signals and equal signal duration. In addition, the maximum observed signal to noise (S/N) ratio from harmonic signals exceeded that of fundamental signals by 50 to 100%. Finally, parallel detection of fundamental and harmonic signals enables deconvolution of overlapping harmonic signals since observed fundamental frequencies can be used to unambiguously calculate all possible harmonic frequencies. Thus, the present application of parallel fundamental and harmonic signal acquisition offers a general approach to improve utilization of harmonic signals to yield high-resolution spectra with decreased acquisition time.

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Graphical Abstract ?

     

Dual signal amplification strategy for amperometric aptasensing using hydroxyapatite nanoparticles. Application to the sensitive detection of the cancer biomarker platelet-derived growth factor BB

The authors describe a dual signal amplification strategy for improving the sensitivity of electrochemical aptasensor. Hydroxyapatite nanoparticles (HAP-NPs) serve as the support for deposition of the respective aptamer. Both the HAP-NPs and the aptamer contain phosphate groups which can react with molybdate to form a redox-active molybdophosphate precipitate on the surface of a glassy carbon electrode (GCE). On applying a relatively low voltage of 0.21 V (vs. Ag/AgCl), a current is generated whose intensity depends on the concentration of the analyte. The cancer biomarker platelet-derived growth factor BB (PDGF-BB) is chosen as a model antigen (analyte). The assay works by sequential deposition of antibody against PDGF-BB, analyte (PDGF-BB) and anti-PDGF-BB aptamer modified HAP-NPs on the GCE to form a sandwich structure. The amperometric signal is linear in the 0.1 pg.mL^?1 to 10 ng.mL^?1 PDGF-BB concentration range, with a detection limit as low as 50 fg.mL^?1. The assay was successfully applied to the determination of PDGF-BB in serum samples. In our perception, this signal amplification strategy has a wide scope in that it can be adapted to the preparation of other aptasensors for biomarkers and related species.

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Graphical abstract Schematic of an electrochemical aptasensor based on dual signal amplification strategy. It was applied to the detection of cancer biomarker platelet-derived growth factor BB (PDGF-BB). Hydroxyapatite (HAP) nanoparticles were chosen for the immobilization of aptamers to increase the loading of aptamers.

     

Redox cycling in nanofluidic channels using interdigitated electrodes

Amperometric detection is ideally suited for integration into micro- and nanofluidic systems as it directly yields an electrical signal and does not necessitate optical components. However, the range of systems to which it can be applied is constrained by the limited sensitivity and specificity of the method. These limitations can be partially alleviated through the use of redox cycling, in which multiple electrodes are employed to repeatedly reduce and oxidize analyte molecules and thereby amplify the detected signal. We have developed an interdigitated electrode device that is encased in a nanofluidic channel to provide a hundred-fold amplification of the amperometric signal from paracetamol. Due to the nanochannel design, the sensor is resistant to interference from molecules undergoing irreversible redox reactions. We demonstrate this selectivity by detecting paracetamol in the presence of excess ascorbic acid. Figure  

Recent progress in electrochemical sensing of cardiac troponin by using nanomaterial-induced signal amplification

Cardiac troponin (cTn) is a specific and sensitive biomarker for diagnosis of myocardial injury. Hence, numerous kinds of biosensors for cTn have been reported. Electrochemical methods possess inherent advantages over other kinds of sensors because they are specific, sensitive, and simple. By combining the advantages of electrochemical biosensors with those of nanomaterials, some interesting electrochemical biosensor for cTn can be obtained where the nanomaterials trigger substantial signal amplification. This review (with 101 refs.) summarizes the state of the art in electrochemical biosensing of cTn based on the use of nanomaterials. Following an introduction into the field, the use of nanomaterials in electrochemical sensing is briefly discussed. A next section covers strategies for signal amplification by using nanomaterials, with subsections on the use of nanowires, nanotubes, graphenes, and various other nanoparticles. The article concludes with a discussion of the prospects of nanomaterial-based signal amplification and on future research directions.

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Graphical abstract Illustration of electrochemical biosensing of cardiac troponin (cTn) with various kinds of nanomaterials, including nanowires, nanotubes, graphene and nanoparticles, as the signal amplification modules.

     

All on size-coded single bead set: a modular enrich-amplify-amplify strategy for attomolar level multi-immunoassay

Ultrasensitive protein analysis is of great significance for early diagnosis and biological studies. The core challenge is that many critical protein markers at extremely low aM to fM levels are difficult to accurately quantify because the target-induced weak signal may be easily masked by the surrounding background. Hence, we propose herein an ultrasensitive immunoassay based on a modular Single Bead Enrich-Amplify-Amplify (SBEAA) strategy. The highly efficient enrichment of targets on only a single bead (enrich) could confine the target-responsive signal output within a limited tiny space. Furthermore, a cascade tyramide signal amplification design enables remarkable in situ signal enhancement just affixed to the target. As a result, the efficient but space-confined fluorescence deposition on a single bead will significantly exceed the background and provide a wide dynamic range. Importantly, the SBEAA system can be modularly combined to meet different levels of clinical need regarding the detection sensitivity from aM to nM. Finally, a size-coded SBEAA set (SC-SBEAA) is also designed that allows ultrasensitive multi-immunoassay for rare samples in a single tube.

A modular single bead enrich-amplify-amplify strategy is proposed for simultaneous detection of multiple proteins at the aM level.