Preparation and full characterization of a micro-immunoaffinity monolithic column and its in-line coupling with capillary zone electrophoresis with Ochratoxin A as model solute

Immunoaffinity Extraction and Alternative Approaches for the Analysis of Toxins in Environmental, Food or Biological Matrices

The evolution of instrumentation in terms of separation and detection allowed a real improvement of the sensitivity and analysis time. However, the analysis of ultra-traces of toxins in complex samples requires often a step of purification and even preconcentration before their chromatographic analysis. Therefore, immunoaffinity sorbents based on specific antibodies thus providing a molecular recognition mechanism appear as powerful tools for the selective extraction of a target molecule and its structural analogs to obtain more reliable and sensitive quantitative analysis in environmental, food or biological matrices. This review focuses on immunosorbents that have proven their efficiency in selectively extracting various types of toxins of various sizes (from small mycotoxins to large proteins) and physicochemical properties. Immunosorbents are now commercially available, and their use has been validated for numerous applications. The wide variety of samples to be analyzed, as well as extraction conditions and their impact on extraction yields, is discussed. In addition, their potential for purification and thus suppression of matrix effects, responsible for quantification problems especially in mass spectrometry, is presented. Due to their similar properties, molecularly imprinted polymers and aptamer-based sorbents that appear to be an interesting alternative to antibodies are also briefly addressed by comparing their potential with that of immunosorbents.

Pre-Concentration and Analysis of Mycotoxins in Food Samples by Capillary Electrophoresis

Mycotoxins are considered one of the most dangerous agricultural and food contaminants. They are toxic and the development of rapid and sensitive analytical methods to detect and quantify them is a very important issue in the context of food safety and animal/human health. The need to detect mycotoxins at trace levels and to simultaneously analyze many different mycotoxin types became mandatory to protect public health. In fact, European Commission regulations specified both their limits in foodstuffs and official sample preparation protocols in addition to analytical methods to verify their presence. Capillary Electrophoresis (CE) includes different separation modes, allowing many versatile applications in food analysis and safety. In the context of mycotoxins, recent advances to improve CE sensitivity, particularly pre-concentration techniques or miniaturized systems, deserve remarkable attention, as they provide an interesting approach in the analysis of such contaminants in complex food matrices. This review summarizes the applications of CE combined with different pre-concentration approaches, which have been proposed in the literature (mainly) in the last ten years. A section is also dedicated to recent microchip–CE devices since they represent the most promising CE mode for this application.

Selective tools for the solid-phase extraction of Ochratoxin A from various complex samples: immunosorbents, oligosorbents, and molecularly imprinted polymers

The evolution of instrumentation in terms of separation and detection has allowed a real improvement of the sensitivity and the analysis time. However, the analysis of ultra-traces of toxins such as ochratoxin A (OTA) from complex samples (foodstuffs, biological fluids…) still requires a step of purification and of preconcentration before chromatographic determination. In this context, extraction sorbents leading to a molecular recognition mechanism appear as powerful tools for the selective extraction of OTA and of its structural analogs in order to obtain more reliable and sensitive quantitative analyses of these compounds in complex media. Indeed, immunosorbents and oligosorbents that are based on the use of immobilized antibodies and of aptamers, respectively, and that are specific to OTA allow its selective clean-up from complex samples with high enrichment factors. Similar molecular recognition mechanisms can also be obtained by developing molecularly imprinted polymers, the synthesis of which leads to the formation of cavities that are specific to OTA, thus mimicking the recognition site of the biomolecules. Therefore, the principle, the advantages, the limits of these different types of extraction tools, and their complementary behaviors will be presented. The introduction of these selective tools in miniaturized devices will also be discussed.

In-line coupling of an aptamer based miniaturized monolithic affinity preconcentration unit with capillary electrophoresis and Laser Induced Fluorescence detection

A composite 30-cm capillary was prepared. The head of the capillary was a 1.5-cm original and miniaturized aptamer-based monolithic affinity support that was in-line coupled to the end of the capillary used for capillary electrophoresis (CE) with laser induced fluorescence (LIF) detection. The device was used for the preconcentration, separation and quantification of ochratoxin A (OTA) as a test solute. The 1.5-cm preconcentration unit consists of a fritless affinity monolithic bonded with 5'-SH-modified oligonucleotide aptamers. A vinyl spacer was used for thiol-ene photoclick chemistry with a 5min irradiation at 365nm. Photografting allowed to confine the binding reaction to the desired silica monolithic segment, upstream the empty section of the CE capillary using an UV mask. The photografting procedure was optimized preparing 10-cm capillary monoliths for nano-LC. The retention factors of cationic solutes in ion-exchange nano-LC allowed to follow the aptamer binding on the monolith. The reproducibility of the photografting process was satisfactory with inter-capillary variation lower than 10%. The aptamer bonding density can be increased by successive graftings of 100μM aptamer concentration solution (5pmol/cm/grafting). The optimal conditions to successfully perform the in-line coupling (preconcentration, elution and separation of OTA) with the composite capillary were adjusted depending on individual requirements of each step but also insuring compatibility. Under optimized conditions, OTA was successfully preconcentrated and quantified down to 0.1pg (percolation of 2.65μL of a 40ng/L OTA solution). A quantitative recovery of OTA (93±2%) was achieved in a single elution of 30pg percolated OTA amount. The reproducibility of the overall process was satisfactory with a relative standard deviation lower than 10% with negligible non-specific adsorption. This device was applied for the preconcentration and analysis of OTA in beer and wine at the ppb level within a total analysis time of 30min.

Photografting as a versatile, localizable, and single-step surface functionalization of silica-based monoliths dedicated to microscale separation techniques

In this work, we developed a surface functionalization way of silica monoliths with a rapid, simple, versatile, and localizable photografting step. The elaboration of a photoreactive layer at the surface of monoliths was first optimized. The functionalization with [γ-(methacryloyloxy)propyl]trimethoxysilane at 80°C in a hydro-organic solution containing triethylamine as catalyst allows reachng the highest density of methacrylate photoactive moieties on silica surfaces. These methacrylate reactive surfaces were subsequently photografted within few minutes with acrylate monomers bearing alkyl chains (C12 and C18). The photografting efficiency was determined by monitoring the retentive properties of monoliths in the RP mode. The retention factors are of the same order of magnitude as highly retentive columns obtained by modification of silica surface with long-alkyl chain silanes or by thermal polymerization of long-alkyl chain monomers. It was also verified that such grafting neither impaired the efficiency of the monolithic stationary phase (Hmin = 6-8 μm in nano-LC) nor its permeability (about 6 × 10(-14) m(2)). Further, it was also demonstrated that photografting is localizable in nonmasked defined areas. Results obtained in anion-exchange chromatography after photopolymerization of [2-(methacryloyloxy)ethyl]trimethylammonium chloride are presented as well to demonstrate the versatility of the developed approach.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2010-2012)

CE has been alive for over two decades now, yet its sensitivity is still regarded as being inferior to that of more traditional methods of separation such as HPLC. As such, it is unsurprising that overcoming this issue still generates much scientific interest. This review continues to update this series of reviews, first published in Electrophoresis in 2007, with updates published in 2009 and 2011 and covers material published through to June 2012. It includes developments in the field of stacking, covering all methods from field amplified sample stacking and large volume sample stacking, through to isotachophoresis, dynamic pH junction and sweeping. Attention is also given to online or inline extraction methods that have been used for electrophoresis.

Characterization of three amino-functionalized surfaces and evaluation of antibody immobilization for the multiplex detection of tumor markers involved in colorectal cancer

Antibody microarrays are powerful and high-throughput tools for screening and identifying tumor markers from small sample volumes of only a few microliters. Optimization of surface chemistry and spotting conditions are crucial parameters to enhance antibodies' immobilization efficiency and to maintain their biological activity. Here, we report the implementation of an antibody microarray for the detection of tumor markers involved in colorectal cancer. Three-dimensional microstructured glass slides were functionalized with three different aminated molecules ((3-aminopropyl)dimethylethoxysilane (APDMES), Jeffamine, and chitosan) varying in their chain length, their amine density, and their hydrophilic/hydrophobic balance. The physicochemical properties of the resulting surfaces were characterized. Antibody immobilization efficiency through physical interaction was studied as a function of surface properties as well as a function of the immobilization conditions. The results show that surface energy, steric hindrance, and pH of spotting buffer have great effects on protein immobilization. Under optimal conditions, biological activities of four immobilized antitumor marker antibodies were evaluated in multiplex immunoassay for the detection of the corresponding tumor markers. Results indicated that the chitosan functionalized surface displayed the highest binding capacity and allowed to retain maximal biological activity of the four tested antibody/antigen systems. Thus, we successfully demonstrated the application of amino-based surface modification for antibody microarrays to efficiently detect tumor markers.

Developments in mycotoxin analysis: an update for 2011-2012

This review highlights developments in mycotoxin analysis and sampling over a period between mid-2011 and mid- 2012. It covers the major mycotoxins aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxin, patulin, trichothecenes, and zearalenone. A section on mycotoxins in botanicals and spices is also included. Methods for mycotoxin determination continue to be developed using a wide range of analytical systems ranging from rapid immunochemical-based methods to the latest advances in mass spectrometry. This review follows the format of previous reviews in this series (i.e. sections on individual mycotoxins), but due to the rapid spread and developments in the field of multimycotoxin methods by liquid chromatography-tandem mass spectrometry, a separate section has been devoted to advances in this area of research.