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[en] Since the advent of microfabrication technology and soft lithography, the lab-on-a-chip concept has emerged as a state-of-the-art miniaturized tool for conducting the multiple functions associated with micro total analyses of nucleic acids, in series, in a seamless manner with a miniscule volume of sample. The enhanced surface-to-volume ratio inside a microchannel enables fast reactions owing to increased heat dissipation, allowing rapid amplification. For this reason, PCR has been one of the first applications to be miniaturized in a portable format. However, the nature of the basic working principle for microscale PCR, such as the complicated temperature controls and use of a thermal cycler, has hindered its total integration with other components into a micro total analyses systems (μTAS). This review (with 179 references) surveys the diverse forms of PCR microdevices constructed on the basis of different working principles and evaluates their performances. The first two main sections cover the state-of-the-art in chamber-type PCR microdevices and in continuous-flow PCR microdevices. Methods are then discussed that lead to microdevices with upstream sample purification and downstream detection schemes, with a particular focus on rapid on-site detection of foodborne pathogens. Next, the potential for miniaturizing and automating heaters and pumps is examined. The review concludes with sections on aspects of complete functional integration in conjunction with nanomaterial based sensing, a discussion on future prospects, and with conclusions. .
[en] Graphene oxide (GO) is often quantified via its UV absorption, typically at around 230 nm. This is convenient but the effect of the size of GO on the accuracy of this method has been ignored so far. The authors report that the molar absorbance of GO is size-dependent. Data are presented on the absorbance of small (hydrodynamic diameter 1 μm), medium sized (1.5 μm), and large (2.2 μm) GO particles at wavelengths of 210, 230 and 250 nm. In general, linear relationship and good regression fits are obtained, but with different slope depending on size even at the same wavelength. This implies that using the UV absorption-based calibration may cause significant errors in GO quantification. Ultimately, this leads to incorrect dosages and faulty conclusions. This may also explain a variety of inconsistent results obtained in previous biological applications of GO. .
[en] Phosphorylated p53 proteins are biomarkers with clinical utility for early diagnosis of cancer, but difficult to quantify. An inductively coupled plasma mass spectrometry (ICP-MS) based immunoassay is described here that uses uniform lanthanide nanoparticles (NPs) as elemental tags for the simultaneous determination of two phosphorylated p53 proteins. Apoferritin templated europium (Eu) phosphate (AFEP) NPs and apoferritin templated lutetium (Lu) phosphate (AFLP) NPs with 8 nm in diameter were used to label two phosphorylated p53 proteins at serine 15 and serine 392 sites (p-p5315 and p-p53392), respectively. The assay has a sandwich format, and p-p5315 and p-p53392 were first captured and then recognized by AFEP and AFLP NPs labelled antibodies, respectively. The Eu and Lu were then released from the immune complexes under acidic condition for ICP-MS measurement. The limits of detection for p-p5315 and p-p53392 are 200 and 20 pg·mL−1, with linear ranges of 0.5–20 and 0.05–20 ng·mL−1, respectively. The method was further applied to study the response of p-p5315 and p-p53392 in SCC-7 cells exposed to the natural carcinogen arsenite. A significant up-regulation of p-p5315 and p-p53392 can be observed when cells were exposed to arsenite at 5 μmol·L−1 level for 24 h. .
[en] In this review, an introduction is given to provide the fundamental principles of magnetic droplet microfluidics. This is followed by a thorough discussion of methods that have been developed for the continuous generation of magnetic droplets and their controlled and precise manipulation by using external magnetic fields. Next, attention is given to techniques devised for the continuous fabrication of magnetic materials in droplets with an emphasis on the synthesis and modification of magnetic nanoparticles (MNPs), magnetic microstructures, Janus microparticles and magnetic hydrogels. In addition, selected applications of continuous magnetic droplets in (bio)assays and detection methods are discussed. The review (with 113 refs.) ends with concluding remarks and a discussion of current challenges and the future outlook for the field of continuous magnetic droplet microfluidics. .
[en] The authors describe a method for synthesis of a nanomaterial consisting of porous carbon encapsulated Mg-Al-Si alloy (denoted as Mg-Al-Si@PC) nanocluster. The nanocluster was synthesis by a solvothermal reaction, followed by high-temperature annealing. The nanoclusters were used as a novel immobilization platform for electrochemical sensing of rutin. The electrochemical behavior of rutin at a modified electrode was investigated by cyclic voltammetry and differential pulse voltammetry. The modified electrode demonstrates a high electrocatalytic activity toward rutin oxidation at a relatively low working potential (0.6 vs. Ag/AgCl). Under optimal conditions, the sensor has a linear response in the 1–10 μM rutin concentration range, and a 0.01 μM lower detection limit (at an S/N ratio of 3). It was successfully applied to the quantification of rutin in pharmaceutical tablets, and satisfactory results were obtained. Furthermore, the results correspond with those with the standard method and with the amounts indicated by the producer, respectively. .
[en] The authors describe an isothermal and ultrasensitive colorimetric DNA assay that consists of two amplification stages using enzymes and a catalytic hairpin assembly (CHA). The first step consists in the selective amplification of DNA using Klenow fragment and nicking enzyme. The second step consists in the amplification of the optical signal by using a catalytic hairpin assembly. After two amplification steps, the DNA reaction induces the aggregation of the red gold nanoparticles to give a blue color shift. The degree of aggregation can be quantified by measurement of the ratio of the UV-vis absorbances of the solutions at 620 and 524 nm which are the wavelengths of the aggregated gold nanoparticles and bare gold nanoparticles. The detection limit is as low as 3.1 fM. Due to the use of a specific enzyme, only the desired DNAs will be detected. The method can be applied to the determination of DNA of various lengths. Despite the presence of large amounts of wildtype DNA, it can readily detect a target DNA. Conceivably, the technique has a large potential because of its high sensitivity and selectivity. .
[en] This review (with 340 refs) focuses on methods for specific and sensitive detection of metabolites for diagnostic purposes, with particular emphasis on electrochemical nanomaterial-based sensors. It also covers novel candidate metabolites as potential biomarkers for diseases such as neurodegenerative diseases, autism spectrum disorder and hepatitis. Following an introduction into the field of metabolic biomarkers, a first major section classifies electrochemical biosensors according to the bioreceptor type (enzymatic, immuno, apta and peptide based sensors). A next section covers applications of nanomaterials in electrochemical biosensing (with subsections on the classification of nanomaterials, electrochemical approaches for signal generation and amplification using nanomaterials, and on nanomaterials as tags). A next large sections treats candidate metabolic biomarkers for diagnosis of diseases (in the context with metabolomics), with subsections on biomarkers for neurodegenerative diseases, autism spectrum disorder and hepatitis. The Conclusion addresses current challenges and future perspectives. .
[en] The review (with 95 refs.) starts with an introduction that addresses the need for magnetic actuation in microfluidics. A second section describes the equations governing magnetic micromixing, with subsections on magnetic equations, fluid flow equations, and on convection–diffusion equations. The next section specifically covers magnetically actuated micromixers, with subsections on those actuated by external permanent magnets, by electromagnets, by microstirrers, and on micromixers with integrated electrodes. The conclusion summarizes the state of the art and addresses current challenges and trends. .
[en] Authors report on a carbon nanotube (CNT)-based lateral flow immunoassay (LFI) for ultrasensitive detection of proteins. Shortened multiwalled CNTs were used as a colored (black) tag. The detection antibody was covalently immobilized on the CNT surface via diimide-activated conjugation between the carboxyl groups on the CNT surface and amino groups of antibodies. The assay involved the capture of target protein in a sandwich-type format between an immobilized capture antibody on the test zone of LFI and a CNT-labelled detection antibody. CNTs were thus captured on the test zone of the LFI and gave a black colored line to enable visual detection of protein. Quantitative results were obtained by reading the test line intensities with a portable strip reader. Rabbit IgG was used as a model target to demonstrate the proof-of-concept. Combining the advantages of lateral flow assay with the unique physical properties of CNT (color, high aspect-to-size ratio and ease of surface modification), the optimized LFI can detect of 1.3 pg mL−1 of rabbit IgG (S/N = 3). This is three orders lower than that of gold nanoparticle-based LFI. Rabbit IgG spiked into human plasma samples was successfully detected with this LFI. Conceivably, this method can be extended to various other proteins for which adequate antibodies do exist. .
[en] 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. < Image>.