Minimal Size of Coffee Ring Structure

Institute of Microelectronics, Peking University, Beijing, PR China.
The Journal of Physical Chemistry B (Impact Factor: 3.3). 03/2010; 114(16):5269-74. DOI: 10.1021/jp912190v
Source: PubMed


A macroscopic evaporating water droplet with suspended particles on a solid surface will form a ring-like structure at the pinned contact line due to induced capillary flow. As the droplet size shrinks, the competition between the time scales of the liquid evaporation and the particle movement may influence the resulting ring formation. When the liquid evaporates much faster than the particle movement, coffee ring formation may cease. Here, we experimentally show that there exists a lower limit of droplet size, D(c), for the successful formation of a coffee ring structure. When the particle concentration is above a threshold value, D(c) can be estimated by considering the collective effects of the liquid evaporation and the particle diffusive motion within the droplet. For suspended particles of size approximately 100 nm, the minimum diameter of the coffee ring structure is found to be approximately 10 microm.

Download full-text


Available from: Tak Sing Wong
  • Source
    • "In many cases, the coffee ring effect is undesired because it causes a non-uniform deposition of entities. Extensive attempts have been made to eliminate the coffee ring effect using the Marangoni effect [23], capillary repulsion [24], addition of surfactant [25], and control of the droplet size [20]. In contrast, earlier studies were also made to take advantage on the self-driven capillary flow for handling biological entities, such as chromatographic separation [26], protein-based diagnoses [27] [28] [29] [30], and preparation of biological fluids [31]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate a method for the detection of nucleic acid using hybridization-induced suppression of the coffee ring effect. When a sessile droplet is pinned on a solid surface, evaporation induces an outward capillary flow that moves suspended particles toward the periphery of the droplet and leaves a ring-shape structure. Compared with spherical particles that are carried to the contact line and form rings, non-spherical particles tend to adhere to each other at the air–water interface where they gain enhanced resistance to the capillary flow and suppress the coffee ring effect. Here, we used suspended microspheres surface-functionalized with single-strand oligonucleotide probes that were complementary to a target DNA. The present target DNA hybridized with the oligonucleotide probe and connected with multiple microspheres, leading to the generation of non-spherical particle agglomerates that resist the capillary flow and form a more uniform deposition of particles after evaporation. Video microscopy and numerical simulation showed that the suppression is because non-spherical particle agglomerates distorted the meniscus surrounding them and exerted a long-range capillary attraction that enhanced the fluidic resistance. Eventually, the microscale hybridization events were translated into the change of coffee ring patterns at macroscale. Using coffee rings as the readout, proof-of-principle studies showed effective sensitivity at low concentrations of 10–100 nM with a wide dynamic range from 10−5 M to 10−8 M, and high specificity that can distinguish the sequence with a single mismatched nucleotide. Owing to the simplicity of the operation and visual readout without the need of a special detector, our approach demonstrates immense potential for the inexpensive and convenient detection of nucleic acid in at resources-limited settings.
    Full-text · Article · Jan 2015 · Sensors and Actuators B Chemical
  • Source
    • "00, Nr. 0, 2014 N:Nanoscale Food Science Chloramphenicol analysis by MIPs–SERS . . . the coin not only provided the substrate for dendritic silver, but also formed a uniform coat tightly adhering to the coin surface to avoid fragmentation, which was reported to occur when depositing onto a bare slide (Lin and others 2004). We blow-dried the solution of CAP spotted on silver dendrite to shorten the drying time and this procedure could also prevent the generation of " coffee ring " (Shen and others 2010) of solution containing target molecule (for example, CAP), which may produce normal Raman signal. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We integrated molecularly imprinted polymers with surface-enhanced Raman spectroscopy (MIPs-SERS) to develop an innovative nano-biosensor for the determination of chloramphenicol (CAP) in milk and honey products. Template molecule (CAP), functional monomer (acrylamide), cross-linking agent (ethylene glycol dimethacrylate), initiator (2,2'-azobis(isobutyronitrile)), and porogen (methanol) were employed to form MIPs via "dummy" precipitation polymerization. Static and kinetic studies validated the specific selectivity of MIPs toward CAP over nonimprinted polymers (imprinting factor >4). Canadian penny-based silver nano-structure was synthesized as SERS-active substrate for determination of CAP in food matrices. Collected spectra were processed by principal component analysis to differentiate various concentrations of CAP in foods. Partial least squares regression models showed good prediction values (R > 0.9) of actual spiked contents (0, 0.1, 0.5, 1, 5 ppm) of CAP in milk and honey. This developed nano-biosensor is low cost, requires little sample pretreatment, and can provide reliable detection of trace level of chemical hazards in food systems within a total of 15 min.
    Full-text · Article · Nov 2014 · Journal of Food Science
  • Source
    • "The prepared gas sensors are based on modulation of the resistance of the WO 3 nanowires that fill the gaps and percolate between the Pt electrodes. Dried WO 3 nanowire droplets have a thick outer border caused by a common coffee ring effect [40] [41], while in the middle section, a tangled but thinner layer of the nanowires forms (Fig. 2). Based on FESEM and EFTEM micrographs, the diameter of the nanowires has relatively large variation from ∼20 to ∼200 nm. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The emerging hydrogen economy has created a demand for the development of improved hydrogen sensors operating at room temperature. In this work, we present hydrogen detectors based on metal decorated WO3 nanowires that were able to detect 1000 ppm of H2, even at room temperature (30 °C), with relatively short recovery time and high sensitivity. The nanowires were synthesized by a hydrothermal process and decorated with PdO and PtOx nanoparticles by decomposition of Pd(acac)2 and Pt(acac)2 precursors. The gas responses were tested for H2, NO, H2S and CO analyte gases in an air buffer at 150, 200 and 250 °C (H2 also at 30, 70 and 130 °C).
    Full-text · Article · Sep 2013 · Sensors and Actuators B Chemical
Show more