Managing Heart Failure at Home With Point-of-Care Diagnostics

Abstract

The objective of this paper is development of an inexpensive point-of-care sensor for detecting the primary heart failure marker peptide, NT-proBNP. The device technology is based on an antibody sandwich assay, but with three innovative aspects. First, chemical amplification is carried out via oxidation of silver nanoparticles (NPs) attached to signaling antibodies rather than by enzymatic amplification. The electrochemical method is faster and eliminates the need for long-term storage of enzymes. Second, the antibody sandwich is formed on mobile magnetic beads. This enhances the rate of mass transfer of the biomarker and the signaling antibody to the primary detection antibody, which is immobilized on the magnetic beads. Third, the sensor itself is fabricated on a paper platform with screen-printed electrodes. This coupled with assembly by simple paper folding, keeps the cost of the sensor low. Here, we report on two separate assays. The first is based on a simple biotin-streptavidin conjugate, which is a preliminary model for the antibody assay. The results indicate a detection limit of 2.1 pM of silver NPs and an assay time of 7 min. The actual NT-proBNP antibody assay takes somewhat longer, and the dynamic detection range is higher: 2.9-582 nM. On the basis of the results presented in this paper, we conclude that this inexpensive paper-based sensor represents a viable technology for point-of-care testing of NT-proBNP, but nevertheless several challenges remain prior to clinical implementation. These include attaining a lower detection limit and better reproducibility, and optimizing the device for human blood.

Keywords: Diagnostic device; heart failure; paper sensor; point of care technology.

FIGURE 1.

NT-proBNP and BNP are produced in a 1:1 ratio after cleavage of Pro-BNP. Reprinted with permission from J. Am. Coll. Cardiol: Cardiovascular Imaging 2009, 2, 216–225. Copyright 2009 Elsevier.

FIGURE 2.

A two-dimensional projection of the NoSlip. See text for details. Reprinted with permission from ACS Sensors 2016, 1, 40–47. (DOI: 10.1021/acssensors.5b00051). Copyright 2016 American Chemical Society.

FIGURE 3.

Illustration of the operation of the NoSlip. See text for details. Reprinted with permission from ACS Sensors 2016, 1, 40–47. (DOI: 10.1021/acssensors.5b00051). Copyright 2016 American Chemical Society.

FIGURE 4.

Electrochemical ASV results for detection of the -AgNP composite in borate buffered saline (100 mM borate, 100 mM NaCl, pH 7.5) solution using the NoSlip. (a) ASVs recorded for the concentrations of AgNP labels shown in the legend. The inset shows an expanded view of the ASV obtained for 2.1 pM AgNPs. The scan rate was 0.010 V/s, and scans started at −0.70 V and ended at 0.20 V. The ASVs were corrected for a sloping baseline that results from oxygen reduction. (b) Calibration curve showing the correlation between charge (obtained by integrating ASVs like those in (a)) and the concentration of AgNPs. Each data point represents the average of at least three measurements carried out using independently fabricated NoSlips. The error bars represent the standard deviation of those measurements. The black line is the best linear fit to the data points, weighted by the error bars. Reprinted with permission from ACS Sensors 2016, 1, 40–47. (DOI: 10.1021/acssensors.5b00051). Copyright 2016 American Chemical Society.

FIGURE 5.

Formation of the NT-proBNP immunocomposite.

FIGURE 6.

Electrochemical ASV results for detection of the NT-proBNP immunocomposite in borate buffered saline (100 mM borate, 100 mM NaCl, pH 7.5) using the NoSlip. (a) ASVs for the concentrations of NT-proBNP indicated in the legend. The scan rate was 0.060 V/s, and scans started at −0.70 V and ended at 0.20 V. The ASVs were corrected for a sloping baseline that results from oxygen reduction. (b) Calibration curve showing the correlation between charge (obtained by integrating ASVs like those in (a)) and the concentration of NT-proBNP. Each data point represents the average of at least three measurements carried out using independently fabricated NoSlips. The error bars represent the standard deviation of those measurements. The data were treated using Dixon’s Q test.