Quantitation of IgE and carcinoembryonic antigen (CEA) by optical beam deflection (OBD) measurement of dot-immunobinding assay patterns visualized by an ELISA technique

Screen-printed electrode produced by printed-circuit board technology. Application to Cancer Biomarker Detection by means of plastic antibody as sensing material

This research work presents, for the first time, a screen-printed electrode (SPE) made on a PCB board with silver tracks (Ag) and a three electrode configuration (AgxO-working, AgxO-counter and Ag/AgxO-reference electrodes), following the same approach as printed-circuit boards (PCBs). This low cost and disposable device was tested for screening a cancer biomarker in point-of-care. The selected biomarker was carcinogenic embryonic antigen (CEA) protein, routinely used to follow-up the progression of specific cancer diseases. The biosensor was constructed by assembling a plastic antibody on the Ag-working electrode area, acting as the biorecognition element of the device. The protein molecules that were entrapped on the polymer and positioned at the outer surface of the polypyrrole (PPy) film were removed by protease action. The imprinting effect was tested by preparing non-imprinted (NPPy) material, including only PPy as biorecognition element. Infrared and Raman studies confirmed the surface modification of these electrodes. The ability of the sensing material to rebind CEA was measured by several electrochemical techniques: cyclic voltammetry (CV), impedance spectroscopy (EIS) and square wave voltammetry (SWV). The linear response ranged from 0.05 to 1.25 pg/mL against logarithm concentration. Overall, producing screen-printed electrodes by means of conventional PCB technology showed promising features, mostly regarding cost and prompt availability. The plastic antibody-based biosensor also seems to be a promising tool for screening CEA in point-of-care, with low response time, low cost, good sensitivity and high stability.

Microchip-based immunoassay system with branching multichannels for simultaneous determination of interferon-gamma

A bead-bed immunoassay system suitable for simultaneous assay of multiple samples was constructed on a microchip. The chip had branching multichannels and four reaction and detection regions; the constructed system could process four samples at a time with only one pump unit. Interferon gamma was assayed by a 3-step sandwich immunoassay with the system coupled to a thermal lens microscope as a detector. The biases of the signal intensities obtained from each channel were within 10%, and coefficients of variation were almost the same level as the single straight channel assay. The assay time for four samples was 50 min instead of 35 min for one sample in the single-channel assay; hence higher throughput was realized with the branching structure chip.

Determination of carcinoembryonic antigen in human sera by integrated bead-bed immunoassay in a microchip for cancer diagnosis

A bead-bed immunoassay system was structured on a microchip and applied to determine carcinoembryonic antigen (CEA), which is a commonly used marker of colon cancer. Polystyrene beads precoated with anti-CEA antibody were introduced into a microchannel, and then a serum sample containing CEA, the first antibody, and the second antibody conjugated with colloidal gold were reacted successively. The resulting antigen-antibodies complex, fixed on the bead surface, was detected using a thermal lens microscope (TLM). A highly selective and sensitive determination of an ultratrace amount of CEA in human sera was made possible by a sandwich immunoassay system that needs three antibodies for an assay. A detection limit dozens of times lower than the conventional ELISA was achieved. Moreover, when serum samples for 13 patients were assayed with this system, there was a high correlation (r = 0.917) with the conventional ELISA. The integration reduced the time necessary for the antigen-antibody reaction to approximately 1%, thus shortening the overall analysis time from 45 h to 35 min. Moreover, troublesome operations required for conventional heterogeneous immunoassays could be much simplified. This microchip-based diagnosis system is the first microchip-based system that is practically useful for clinical diagnoses with short analysis time, high sensitivity, and easy procedures.

Integration of an immunosorbent assay system: analysis of secretory human immunoglobulin A on polystyrene beads in a microchip

An immunosorbent assay system was integrated into a glass microchip. Polystyrene beads were introduced into a microchannel, and then human secretory immunoglobulin A (s-IgA) adsorbed on the bead surface was reacted with colloidal gold conjugated anti-s-IgA antibody and detected by a thermal lens microscope. The scale merits of liquid microspace on the molecular behavior remarkably contributed to reduced assay time. The integration cut the time necessary for the antigen-antibody reaction by 1/90, thus shortening the overall analysis time from 24 h to less than 1 h. Moreover, troublesome operations required for conventional immunosorbent assays could be replaced by simple operations.

Rapid detection of specific polyclonal and monoclonal antibodies against bovine leukemia virus

ELISA and Western blot have been used for detecting specific antibodies or antigens for routine diagnostic laboratory tests and experimental protocols, as well as for screening hybridomas secreting antibodies. Although these techniques are sensitive, some slow growing hybridomas are identified as positive only when they are grown slowly long time. We standardized the dot-ELISA, a more sensitive technique, for the detection of antibodies against BLV. The main advantages of the dot-ELISA described in this study are (a) its sensitivity, detecting hybridomas which would otherwise be considered negative and discarded from the results of indirect ELISA and/or Western blot; and (b) the possibility of economizing reagents using as little as 1 microl of the antigen and 0.5 microl of antibody and conjugate. Different BLV-antigen preparations were bound to nitrocellulose membranes (NC), including cells lysed chemically (LYS) or by sonication (SOC), semi-purified virus (PV), and supernatant from infected cultures, either without treatment (SUP) or sonicated (SOS). The antigen preparations most adequate for detecting monoclonal antibodies against BLV and polyclonal antibodies in cattle sera were undiluted cell lysates (LYS) and semi-purified BLV (PV). When testing bovine sera, the supernatant (SUP) and sonicated supernatant (SOS) antigens gave a high background due to the presence of FCS which reacted with the anti-bovine labeled antibodies. In this study, 59 BLV specific antibody secreting hybridomas were identified using the dot-ELISA, compared to only 20 detected using iELISA, and doubtful reactions due to nonspecific binding to fetal calf serum (FCS) and cellular components were measured. The results of the improved dot-ELISA described may be stored at room temperature for future reference. Results were consistently reproducible in coated nitrocellulose membranes kept at different storage temperatures (-20 degrees C, 4 degrees C, and 25-30 degrees C) 48 h, 1 week and 5 months.

Ultrasensitive heterogeneous immunoassay using photothermal deflection spectroscopy. 2. Quantitation of ultratrace carcinoembryonic antigen in human sera

We previously proposed a photothermal immunoassay based on highly sensitive detection by a photothermal beam deflection method using colloidal gold as a labeling material. The assay system was significantly improved in terms of background reduction of ultrasensitive laser spectrometry through the newly designed reaction and separation procedure using microspheres for a solid phase. Highly sensitive laser spectrometric analysis is often susceptible to interference by even a small amount of admixtures. In this subsequent study, we improved our photothermal immunoassay so that it possesses further selectivity, matching that of the highly sensitive photothermal detection method. It was proved that our method could be applied to determine ultratrace quantities of a carcinoembryonic antigen (CEA) in cancer patients' and normal sera. The lower detection limit of CEA was 0.078 ng/mL (9.8 amol, absolute quantity). This is 10 times superior to that of any other immunoassay method and has enough detectability to measure a low level of CEA in healthy individuals. Intraassay coefficient of variation is about 8% at eight different concentrations (n = 6). We assayed 61 serum samples, and there was a good correlation between this method and previously established ELISA. We obtained clearer demarcation of healthy persons and colon cancer patients in terms of the CEA value than was obtained by ELISA. We believe this is the first report in which the laser-based ultrasensitive immunoassay is proved to be applicable to human sera, although the matrix admixtures causing interference in the assay were quite different in each sample serum.