Abstract
A simple optical aptasensor has been synthesized for the detection of calcium ions. This sensing approach employs a semiconductor quantum dot (QD)–gold nanoparticle as the donor–quencher pair and operates on the principle of fluorescence resonant energy transfer (FRET). On binding with calcium ions, the DNA aptamer undergoes a conformational change, which changes the distance between the quantum dot and the gold nanoparticle, conjugated on the 5′ terminal and 3′ terminal of the aptamer, respectively. This phenomenon results in the quenching of the quantum dot emission. In this sensor, a maximum quenching of 22.42 ± 0.71% has been achieved at 35 nM calcium ion concentration while the limit of detection has been determined to be 3.77 pM. The sensor has been found to have high specificity for calcium ions in comparison to other metal ions like sodium, magnesium, and potassium. The molecular apta-beacons also demonstrated successful endocytosis and FRET-based calcium ion detection in osteocyte cells when conjugated with a cell-penetrating peptide (DSS).
Highlights
Calcium ions (Ca2+) are an essential component of the physiological system
Nanosep molecular weight cutoff (MWCO) filters of 3 and 100 k pore sizes were purchased from Pall Life Sciences (Ann Arbor, MI)
The external loop was composed of 5 single-strand bases along with 1 closing helix
Summary
Calcium ions (Ca2+) are an essential component of the physiological system. They play a significant role as an intracellular messenger, which regulates several cellular functions like secretion, contraction, excitability, and gene expression (Russell, 2011). An increased Ca2+ release can contribute to diseases like HIV, schizophrenia, and Alzheimer’s disease (Wojda et al, 2008). Owing to the significance of this metal ion in the physiological system, the objective of this study is to design a sensor, which rapidly detects Ca2+. Asif et al reported a zinc oxide nanorod-extended gate field-effect transistor (MOSFET), which detected Ca2+ linearly between 1 μM and 1 mM (Asif et al, 2009). Several analytical techniques for Ca2+ sensing have been published in literature
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