Size-selective detection in integrated optical interferometric biosensors

We present a new size-selective detection method for integrated optical interferometric biosensors that can strongly enhance their performance. We demonstrate that by launching multiple wavelengths into a Young interferometer waveguide sensor it is feasible to derive refractive index changes from different regions above the waveguide surface, enabling one to distinguish between bound particles (e.g. proteins, viruses, bacteria) based on their differences in size and simultaneously eliminating interference from bulk refractive index changes. Therefore it is anticipated that this new method will be ideally suited for the detection of viruses in complex media. Numerical calculations are used to optimize sensor design and the detection method. Furthermore the specific case of virus detection is analyzed theoretically showing a minimum detectable virus mass coverage of 4 × 10(2) fg/mm(2) < (typically corresponding to 5 × 10(1) particles/ml).

Clinical evaluation of a simple image cytometer for CD4 enumeration on HIV-infected patients

BACKGROUND

Affordable, easy-to-use, and reliable CD4(+) T lymphocyte enumeration systems are needed in resource-constrained settings to monitor HIV.

METHODS

A simple image cytometer was used to count fluorescently labeled CD4(+) T and CD8(+) T lymphocytes from CD3 immunomagnetically selected cells on blood specimens of 460 HIV-1-infected patients in Siriraj Hospital, Bangkok, Thailand. Results were compared with flow cytometry (FCM).

RESULTS

CD4(+) T lymphocyte counts by image cytometer were comparable (R > or = 0.97) with those by the FACSCount and the FACScan with a bias of 7.3 and 9.1%, respectively. At very low CD4(+) T lymphocyte counts (< or =50/microl) some over-count outliers were observed by the FACScan and image cytometer when compared with the FACSCount. For CD8 enumeration, the image cytometer showed a good correlation (R = 0.96) and a consistent undercount (approximately 17%) when compared with the FACSCount.

CONCLUSIONS

Evaluation of the image cytometer for CD4 and CD8 enumeration demonstrated comparable results with FCM on a population of HIV-1-infected patients. The image cytometer is a good alternative method for point-of-care settings in resource-constrained countries.

An ultrasensitive young interferometer handheld sensor for rapid virus detection

Future viral outbreaks are a major threat to societal and economic development throughout the world. A rapid, sensitive and easy-to-use test for viral infections is essential to prevent and control such viral pandemics. Furthermore, a compact, portable device is potentially very useful in remote or developing regions without easy access to sophisticated laboratory facilities. In this report we discuss the application of a Young interferometer sensor device for ultrasensitive and real-time detection of viruses. The essential innovation in this technique is the combination of an integrated optical interferometric sensor with antibody-antigen recognition approaches to yield very sensitive, rapid virus detection. The technology is amenable to miniaturization and mass production and, thus, has significant potential to be developed into a handheld, point-of-care device.

CD4+ T lymphocytes enumeration by an easy-to-use single platform image cytometer for HIV monitoring in resource-constrained settings

BACKGROUND

HIV monitoring in resource-constrained settings demands affordable and reliable CD4(+) T lymphocytes enumeration methods. We developed a simple single platform image cytometer (SP ICM), which is a dedicated volumetric CD4(+) T lymphocytes enumeration system that uses immunomagnetic and immunofluorescent technologies. The instrument was designed to be a low-cost, yet reliable and robust one. In this article we test the instrument and the immunochemical procedures used on blood from HIV negative and HIV positive patients.

METHODS

After CD4 immunomagnetic labeling in whole blood, CD4(+) T lymphocytes, CD4(+dim) monocytes and some nonspecifically labeled cells are magnetically attracted to an analysis surface. Combining with CD3-Phycoerythrin (PE) labeling, only CD3(+)CD4(+) T lymphocytes are fluorescently labeled and visible in a fluorescent image of the analysis surface. The number of CD4(+) T lymphocytes is obtained by image analysis. Alternatively, CD3 immunomagnetic selection in combination with CD4 immunofluorescent labeling can also be applied for CD4(+) T lymphocytes enumeration.

RESULTS

The SP ICM system was compared with two single platform flow cytometer (SP FCM) methods: tetraCXP and TruCount methods. The SP ICM system has excellent precision, accuracy and linearity for CD4(+) T lymphocytes enumeration. Good correlations were obtained between the SP ICM and the SP FCM methods for blood specimens of 44 HIV(-) patients, and of 63 HIV(+) patients. Bland-Altman plots showed interchangeability between the SP ICM and the SP FCM methods.

CONCLUSIONS

The immunolabeling methods and the instrumentation are simple and easy-to-handle for less-trained operators. The SP ICM system is a good candidate for CD4(+) T lymphocytes enumeration in point-of-care settings of resource-constrained countries.

A single platform image cytometer for resource-poor settings to monitor disease progression in HIV infection

BACKGROUND

For resource-poor countries, affordable methods are required for enumeration of CD4(+) T lymphocytes of HIV-positive patients. For infants, additional determination of CD4/CD8 ratio is needed.

METHODS

We determine the CD4(+) and CD8(+) T lymphocytes as the CD3(+)CD4(+) and CD3(+)CD8(+) population of blood cells. Target cells are CD3-immunomagnetically separated from the whole blood, and CD4-Phycoerythrin and CD8-PerCP immunofluorescently labeled. A point-of-care single platform image cytometer was developed to enumerate the target CD3(+)CD4(+) and CD3(+)CD8(+) populations. It has light-emitting diodes illumination, is fully computer-controlled, operates from a 12 V battery, and was designed to be cheap and easy-to-handle. Target cells are imaged on a CCD camera and enumerated by an image analysis algorithm. The cytometer outputs the absolute number of CD4(+) and CD8(+) T lymphocytes/microl and CD4/CD8 ratio.

RESULTS

The quality of the cell images obtained with the cytometer is sufficient for a reliable enumeration of target cells. The image cytometer achieves an accuracy of better than 10% in the range of 50-1700 cells/microl. Analysis of blood samples from HIV patients yields a good agreement with the TruCount method for CD4 and CD8 count and CD4/CD8 ratio.

CONCLUSIONS

The image cytometer is affordable (component costs $3,000), compact (25 x 25 x 20 cm(3)), and uses disposable test materials, making it a good candidate to monitor progression of immunodeficiency disease in resource-poor settings.

Fast, ultrasensitive virus detection using a Young interferometer sensor

We report the application of an integrated optical Young interferometer sensor for ultrasensitive, real-time, direct detection of viruses. We have validated the sensor by detecting herpes simplex virus type 1 (HSV-1), but the principle is generally applicable. Detection of HSV-1 virus particles was performed by applying the virus sample onto a sensor surface coated with a specific antibody against HSV-1. The performance of the sensor was tested by monitoring virus samples at clinically relevant concentrations. We show that the Young interferometer sensor can specifically and sensitively detect HSV-1 at very low concentrations (850 particles/mL). We have further demonstrated that the sensor can specifically detect HSV-1 suspended in serum. Extrapolation of the results indicates that the sensitivity of the sensor approaches the detection of a single virus particle binding, yielding a sensor of unprecedented sensitivity with wide applications for viral diagnostics.

Drift correction in a multichannel integrated optical young interferometer

We demonstrate that in a sensor based on a multichannel Young interferometer, the phase information obtained for different pairs of channels can be used to correct the long-term instability (drift) due to temperature differences between measuring and reference channels, the drift in the alignment of the setup, etc. Experiments show that the nature of a major part of the drift is such that the drift present in one of the channels can be determined by interpolation of the drift measured in the two adjacent channels. It is shown that a drift reduction of 10 times can be achieved as compared with the situation in which no correction is applied. We anticipate that these findings will permit the exploitation of the extreme sensitivity of interference-based sensors to a much greater extent.

Integration of microfluidics with a four-channel integrated optical Young interferometer immunosensor

This report describes an optical sensing hybrid system obtained by bonding a microfluidic system to an integrated optical (IO) four-channel Young interferometer (YI) chip. The microfluidic system implemented into a glass plate consists of four microchannels with cross-sectional dimensions of 200 microm x 15 microm. The microfluidic system is structured in such a way that after bonding to the IO chip, each microchannel addresses one sensing window in the four-channel YI sensor. Experimental tests show that the implementation of the microfluidics reduces the response time of the sensor from 100s, as achieved with a bulky cuvette, to 4s. Monitoring the anti-human serum albumine/human serum albumine (alpha-HSA/HSA) immunoreaction demonstrates the feasibility to use the microfluidic sensing system for immunosensing applications. In this case, a better discrimination between the bulk refractive index change and the layer formation can be made, resulting into higher accuracy and offering the prospect of being able to use the kinetics of the immunoreaction. The microfluidic sensing system shows an average phase resolution of 7 x 10(-5) x 2pi for different pairs of channels, which at the given interaction length of 4 mm corresponds to a refractive index resolution of 6 x 10(-8), being equivalent to a protein mass coverage resolution of 20 fg/mm2.

Realization of a multichannel integrated Young interferometer chemical sensor

We report on the design, realization, and characterization of a four-channel integrated optical Young interferometer device that enables simultaneous and independent monitoring of three binding processes. The generated interference pattern is recorded by a CCD camera and analyzed with a fast-Fourier-transform algorithm. We present a thorough theoretical analysis of such a device. The realized device is tested by monitoring glucose solutions that induce well defined phase changes between output channels. The simultaneous measurement of three different glucose concentrations shows the multipurpose feature of such devices. The observed errors, caused by the mismatching of spatial frequencies of individual interference patterns with those determined from the CCD camera, are reduced with different reduction schemes. The phase resolution for different pairs of channels was approximately 1 x 10(-4) fringes, which corresponds to a refractive-index resolution of approximately 8.5 x 10(-8). The measured sensitivity coefficient of the phase change versus refractive-index change of approximately 1.22 x 10(3) x 2pi agrees well with the calculated coefficient of approximately 1.20 x 10(3) x 2pi.