Facile Counting of Ligands Capped on Nanoparticles via a Titration Chip of Moving Reaction Boundary Electrophoresis

Abstract

Absolute quantification of ligand capped on the surface of nanoparticles (NPs) has faced a great challenge without the use of complex inner standards (CIS). Herein, we proposed a facile electrophoresis titration (ET) model, designed an ET device, and developed a relevant method for counting the ligand on NPs without the use of CIS, based on moving reaction boundary (MRB). Furthermore, we conducted the relevant ET runs by using 3-mercaptopropionic acid (MPA) and quantum dots (QDs) as the model ligand and NPs, respectively. The experiments revealed that the ligand content of 1518 ± 295 obtained via an ET was close to the one of 1408 ± 117 determined via NMR, validating the ET model. Moreover, the experiments showed fair stability (RSD < 5.62%) and simplicity of ET without the use of CIS. Evidently, the ET model opens a window for facile assay of ligand capped on NPs.

Model, Simulation, and Experiments on Moving Exchange Boundary via Ligand and Quantum Dots in Chip Electrophoresis

“…However, the exchange of (I) is slow, the balance of interaction takes long time, and the MEB-Q is wide and blurry, indicating difficulty of exact readout of boundary location if without proper boundary definition (sections S2 and S3). This is evidently different from the sharp neutralization boundary. , In MEB-Q, the distributions of bound MPA- on QDs, free DTNB, bound TNB- on QDs, and free MPA among the motion direction of MEB-Q can be described via eqs S9–S12 in line with the previous work . The analytical solutions of eqs S9–S12 are given in the details of eqs S21–S28.…”

“…As a run continues, more DTNB is forced into the zone of [MPA-QDs], and more MPA- is exchanged from [MPA-QDs] by DTNB, quenching [MPA-QDs] fluorescence. The motion of MEB-Q , is described via, where d MEB‑Q is the migration distance of MEB-Q from the initial time of t q1 and the end time of t q2 , v MEB‑Q is the moving rate of MEB-Q, where the c MPA‑ and c DTNB are contents of MPA- on QDs and DTNB in the channel, respectively. However, the exchange of (I) is slow, the balance of interaction takes long time, and the MEB-Q is wide and blurry, indicating difficulty of exact readout of boundary location if without proper boundary definition (sections S2 and S3).…”

“…Identification of the ligand (e.g., MPA- on NPs) via NMR still faced challenges: (i) impossibility of NPs analyses via NMR if without an ultrapure inner standard, (ii) expensive instrument, and (iii) complex sample pretreatment. The challenges were addressed by the MRB concept Figure and ref .…”

“…Electrophoretic techniques have played a key importance in the fields of life science, biomedicine, and bio/nanoparticles. − They have been used for genomic sequence, protein separation and identification, and drug/enzyme screenings . Particularly, they have been applied for separation, capture, identification, and characteristics of bio/nanoparticles, e.g., mitochondrion, microorganism, exosomes, and nanoparticles (NPs) as well as quantum dots (QDs) …”

“…The moving reaction front − has opened the fantastic window of the moving reaction boundary (MRB). , First, the concept of MRB reactivated the development of IEF dynamics and the method. , Second, it initiated the electrophoretic biosensing for food safety . Third, it induced the MRB-based sensing of hemoglobin A1c in diabetes blood and accounting ligands on QDs . However, there was a rare report on the model and simulation on moving exchange boundary (MEB).…”