Enabling electrical biomolecular detection in high ionic concentrations and enhancement of the detection limit thereof by coupling a nanofluidic crystal with reconfigurable ion concentration polarization

Abstract

The regulation effect of surface charges on the transport of electrons in nanomaterials and ions in nanofluidic devices has been widely used to develop highly sensitive and label-free electrical biosensors. The intrinsic limitation to the clinical application of surface charge-effect nano-electrical biosensors is that they usually do not function in physiological conditions normally with high ionic concentrations (~160 mM), in which the surface charges are screened within a short distance (<1 nm at 160 mM). In this work, we developed a general strategy that enables surface charge-effect electrical biomolecular detection in physiological conditions with integrated mechanism for enhancement of limit of detection (LOD) by in-situ preconcentration of target molecules during incubation and creating a transient low ionic concentration environment during the signal readout step using reconfigurable ion concentration polarization (ICP). We demonstrated the effectiveness of this strategy in a facile nanofluidic biosensor named nanofluidic crystal (NFC), which can be prepared within hours and without expensive equipment. Our results indicate that the ion depletion effect of ICP could lower the ionic concentration by at least 200 folds and provide a stable ionic environment for over 15 s, enabling electrical detection of proteins and DNAs in serum and urine with LODs of 1–10 nM. We further reconfigured the device to preconcentrate target biomolecules before detection using the enrichment effect of ICP, obtaining LODs of 10–100 pM for proteins and DNAs in physiological conditions. By overcoming the inherent constraint on buffer conditions and the issues regarding fabrication, we believe this work represents a significant progress towards the practical application of surface charge-effect nano-electrical biosensors in point-of-care diagnostics and clinical medicine.

Recent advances in paper‐based preconcentrators by utilizing ion concentration polarization

“…In this paper, the recent progress of the ICP effect in the preconcentration of microsamples in a paper-based preconcentrator is reviewed, and the basic working principle, applications, and research progress of ICP are introduced. ICP preconcentration is also widely used in microfluidic chips on other substrates, such as PDMS [97,[119][120][121][122][123][124][125][126][127][128], polycarbonate [129], glass [127,[130][131][132][133][134][135], silicon [36,[136][137][138][139], and land hydrogels [140]. In addition, studies have been conducted on ICP preconcentration driven by ion-selective osmotic membrane pressure [141], ICP preconcentration of magnetic nanoparticles and magnets [142], etc.…”

Nanofluidic crystals: nanofluidics in a close-packed nanoparticle array

“…119 The detection of biomolecules in clinical samples was further investigated with the nanofluidic crystal-ICP coupled strategy, which would potentially make it a truly enabling technique for rapid biochemical sensing at the point-of-care. 120 …”

Development and Evaluation of a Quantitative Fluorescent Lateral Flow Immunoassay for Cystatin-C, a Renal Dysfunction Biomarker

“…ELISA requires costly plate readers and these assays are more error-prone due to their tedious operation, limiting their usage in point of care (POC) diagnostics. Other methods such as photoelectrochemical assays [ 17 ], fluorescence [ 18 ], near-infrared spectrometry [ 19 ], and LC-mass spectrometry-based proteomics [ 20 ], microfluidic ELISA [ 21 ], electrokinetic microfluidics [ 22 ], DNA microarray [ 23 ], and microfluidics [ 24 ] are alternative methods for the detection of cystatin-C. However, they are too expensive, technically complex, and time-consuming; they require trained personnel and advanced equipment, making them unsuitable for use at the point of need [ 3 , 25 ].…”