Figures & data
Figure 1 The schematic of the optimized LFIA for BNP detection.
Notes: (A) The structure of previous LFA is adjusted by adding a conjugate pad to form a new type of LFIA. (B) The negative result (i) and positive result (ii) show the principle of the LFIA. (C) The diameter of GNP is adjusted from 13±3 to 35±3 nm. (D) The concentration of test line is adjusted from 0.5 to 1.5 mg/mL.
Abbreviations: GNP, gold nanoparticle; BNP, brain natriuretic peptide; LFA, lateral flow assay; LFIA, lateral flow immunoassay; NC, nitrocellulose.
Figure 2 The effect of improved structure of test strip on LFIA performance.
Notes: (A) The schematic diagrams show the structure of test strip before (i) and after (ii) incorporating a piece of conjugate pad into the test strip. (B) The images (i) of comparison of conventional and improved LFAs and the results (ii) which show that the detection limit is improved from 5 µg/mL to 1 µg/mL (the arrows reference the detection limit of the results).
Abbreviations: LFA, lateral flow assay; LFIA, lateral flow immunoassay; NC, nitrocellulose; C, control line; T, test line.
Figure 3 The effect of antibody concentration at the test line on LFIA performance.
Notes: (A) The schematic diagram and results of the LFIA with 0.5 mg/mL (i) and 1.5 mg/mL coating antibody (ii). (B) Optical density analysis of (A) (n=3, *P<0.05). (The arrows reference the detection limit of the results).
Abbreviations: LFIA, lateral flow immunoassay; NS, no significance; PBS, phosphate-buffered saline; C, control line; T, test line.
Figure 4 The effect of GNP diameter on LFIA performance.
Notes: (A) The schematic diagram and results of the LFIA with 13±3 nm GNP (i) and 35±3 nm GNP (ii). (B) Optical density analysis of (A) (n=3, *P<0.05). (The arrows reference the detection limit of the results).
Abbreviations: GNP, gold nanoparticle; LFIA, lateral flow immunoassay; NS, no significance; PBS, phosphate-buffered saline; C, control line; T, test line.
Figure 5 Sensitivity assay using the optimized LFIA.
Notes: (A) The images showing LFIA results in the detection of different concentrations of BNP solutions. (B) Optical density analysis of (A) (n=3, *P<0.05). (The arrow references the detection limit of the results).
Abbreviations: BNP, brain natriuretic peptide; LFIA, lateral flow immunoassay; NS, no significance; PBS, phosphate-buffered saline; C, control line; T, test line.
Figure 6 Clinical sample testing using the optimized LFIA.
Notes: (A) The sensitivity results of optimized LFIA detect BNP in human sera (the inset shows the images of LFA results in the detection of different concentrations of BNP solutions). (B) The specificity results of optimized LFIA detect BNP in human sera (n=3, *P<0.05) (the inset shows the images of LFA results in the detection of different samples). (The arrow references the detection limit of the results).
Abbreviations: BNP, brain natriuretic peptide; CRP, C-reactive protein; cTnI, troponin I; LFIA, lateral flow immunoassay; Myo, myoglobin; NS, no significance; NT-proBNP, N-terminal fragment of BNP precursor.
Table 1 The recovery rates of other three concentrations of BNP
Figure 7 The calibration curve of relationship between target concentration and optical density.
Figure S1 Characterization of GNP.
Notes: (A) Characterization of GNP with 13 nm: (i) TEM and size distribution of GNP; (ii) UV–vis absorption spectra of GNP. (B) Characterization of GNP with 35 nm: (i) TEM and size distribution of GNP; (ii) UV–vis absorption spectra of GNP.
Abbreviations: GNP, gold nanoparticle; TEM, transmission electron microscopy; UV–vis, ultraviolet–visible.
Figure S2 Determination of optimal pH and volume of conjugation.
Notes: (A) Determination of optimal pH for the conjugation of antibody to GNP (The inset shows the images of color change of pH optimization). (B) Determination of optimal volume of coating antibody for conjugation at pH 8 (The inset shows the images of color change of volume optimization).
Abbreviation: GNP, gold nanoparticle.
