Lateral Flow Assays (LFAs)

Lateral Flow Assays (LFAs) are part of the Point of Care Testing (POCT). LFAs are primarily intended for the clinical analysis of biological samples such as plasma, urine, and saliva.  This test allows the early diagnosis of many diseases and infections to guide the choice of treatment.  The application of Lateral Flow Assays also extends to areas such as agriculture, food, environmental safety, and veterinary medicine.

The Bright-Dtech™ LFAs are based on the migration of detection bioreceptors conjugated to fluorescent nanoparticles along the strip for analytes detection. The resulting signal intensity at the control and test lines is measured by a time-resolved fluorescence reader. This method allows to quantify the targeted analyte with an improved sensitivity.

Figure of Lateral Flow Assays with Bright-Dtech

Lateral Flow Assays by Poly-Dtech allow the detection and quantification of specific biomarkers. The sample is first diluted in the running buffer before being loaded on the sample pad. The running buffer defines the optimal conditions for the detection of the analyte. Then, the sample migrates to the conjugate pad where the Bright-Dtech™-conjugated antibodies are immobilized. Wetting of the conjugate pad allows the release of the detection bioreceptor and the first interaction with the antigen. The resulting antigen-antibody-labelled complex reaches the nitrocellulose membrane. The test line consists of a monoclonal antibody against the antigen, while the control line is composed of species-specific antibodies. After 20 minutes of sample migration, the fluorescent signal emitted at the control and test line is measured using a time-resolved fluorescence reader. The fluorescent signal is proportional to the amount of target in the sample.

Our customized Bright-Dtech™ technology is available for all matched antibody pair developed for classical sandwich ELISA allowing accurate detection and high signal/noise ratio for reliable results.

Why using Bright-Dtech™ for Lateral Flow Assays?

Our technology overcomes the classic disadvantages of Lateral Flow Assays by offering a fast, highly sensitive and photobleaching-free solution through Bright-Dtech™ lanthanide nanoparticles. We have also a low LOD, LLOQ and a low hands-on time. Bright-Dtech™ LFAs allows quantitative and semi-quantitative analysis.

Serological Test

Serological LFAs are used for the detection of targeted antibodies (IgG, IgM, or total) in blood samples. The conjugate pad contains Bright-Dtech™-conjugated antigen or Bright-Dtech™-conjugated rabbit IgG. Anti-IgG or anti-IgM antibodies are striped on the test line, while anti-rabbit IgG antibodies are striped on the control line.

Antigenic test

Antigenic tests are used for the detection of a target analyte in a sample (urine, saliva, sweat, etc.). These tests are run according to two formats: sandwich and competitive.

In a sandwich assay, analytes are captured between the Bright-Dtech-conjugated antibody and the capture antibody located on the test line. This strategy is adapted to the detection of large analytes (> 1 KDa) containing at least two distinct epitopes, thus two binding sites. In this case, the signal obtained on the test line is proportional to the amount of target in the sample.

Competitive formats are typically used to test small molecules with unique antigenic determinants, which cannot bind to two antibodies simultaneously. In this assay, the test line contains the target analyte. The conjugate pad contains Bright-Dtech™-conjugated antibodies able to recognize the analyte on the test line and in the sample. If the target is in the sample, it will bind to the detection bioreceptor and prevent its binding to the test line. The signal obtained in a competitive assay is inversely proportional to the amount of analyte present in the sample.

Example: LFA for PSA detection in sandwich format

PSA (Prostate-Specific Antigen) is the biomarker for detecting prostate cancer. Poly-Dtech’s Lateral Flow Assays allow the quantitative detection of PSA biomarker present in serum.

Strips used to determine standard curve for PSA detection

Figure 1. Strips used to determine standard curve for PSA detection
This figure demonstrates a very low limit of detection of PSA (LOD = 25 pg/mL) through TRF reader, which is the same range of sensitivity as PSA ELISA tests.

After the reading, the test validation allows to establish a standard curve.

Standard curve for PSA detection through Lateral Flow Assays

Figure 2. Standard curve for PSA detection
Results demonstrate a dynamic range between 71 to 65 000 pg/mL.

Example: LFA for SARS-CoV-2 nucleoprotein detection in sandwich format

SARS-CoV-2 is the biomarker for detecting Covid-19 disease. Its presence can be detected through Lateral Flow Assays.

Images of the test sripts for detecting SARS-CoV-2

Figure 3. Images of the test strips for detecting SARS-CoV-2 nucleoprotein.

Bright-Dtech™ based lateral flow assay obtained with a time-resolved fluorescence plate reader. Fluorescence signal is visible from 250 pg/mL to 1000 pg/mL. Clear and consistent control lines are visible.

In addition to its qualitative detection, Poly-Dtech is also able to quantify the SARS-CoV-2 biomarker.

Quantitative detection of SARS-CoV-2 through Lateral Flow Assays

Figure 4. Quantitative detection of SARS-CoV-2 nucleoprotein.

Results demonstrate a very low/significant limit of detection of SARS-Cov-2 (LOD = 0.075ng/mL using 3 standard deviation).