Abstract
The development of highly sensitive and rapid methods for detecting DNA is of critical importance. Here, we describe a strategy for the digital detection of target DNA at the femto-molar level. Individual DNA molecules were encoded with a single gold nanorod (AuNR), separated and enriched by magnetic immune-separation. The coding gold nanorods were then de-hybridized and dispersed into a gold nanosphere (AuNS) solution at a certain concentration, and both gold nanoparticles were immobilized on glass slides for dark-field microscopic imaging. Using an in-house Matlab program, the concentration of the target DNA was calculated based on the ratio of the coding gold nanorods to gold nanospheres. By combining the coding of individual biomolecules with a single gold nanorod and the use of gold nanospheres as an internal standard, a method for the rapid and accurate digital detection of target DNA to the femto-molar level was developed.
Highlights
Were applied to reduce the possibility of multiple attachments of the target DNA to a single AuNR
Magnetic beads functionalized with carboxylic acid groups (2.7 μm in diameter) were purchased from Thermo Fisher Scientific (USA). 3-Aminopropyltriethoxysilane (APTES) was purchased form Nanjing Chen Gong organic silicon material co., LTD (China). 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) was purchased from the Tokyo Kasei Kogyo Co. (Japan), and the EDC solutions used in this work were made immediately prior to use
Due to the localized surface plasmon resonance (LSPR) effect[16,17,18], individual noble metal nanocrystals scatter light strongly with a distinct color, allowing it to be clearly distinguished by a DFM19,20
Summary
Were applied to reduce the possibility of multiple attachments of the target DNA to a single AuNR. A positively charged glass slide modified with an amino-terminated self-assembled monolayer was used to immobilize the negatively charged coding-AuNRs and internal standard AuNSs to overcome Brownian motion through electrostatic interactions, which allowed us to detect the number ratio of the two types of nanocrystals by a dark field microscopy (DFM) (Fig. S1). The concentration of the target DNA, which is in proportional to the coding-AuNRs, was obtained from the number ratio and known concentration of the internal standard nanocrystal
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