Tangential Flow Ultrafiltration: A "Green" Method for the Size Selection and Concentration of Colloidal Silver Nanoparticles

Abstract

Nowadays, AgNPs are extensively used in the manufacture of consumer products, 1 ) than conventional methods of isolation such as ultracentrifugation. 19TFU is a recirculation method commonly used for the weight-based isolation of proteins, viruses and cells. 20,21 Briefly, the liquid sample is passed through a series of hollow fiber membranes with pore size ranging from 1,000 kD to 10 kD. Smaller suspended or dissolved constituents in the sample will pass through the porous barrier together with the solvent (filtrate), while the larger constituents are retained (retentate). TFU may be considered a "green" method as it neither damages the sample nor requires additional solvent to eliminate toxic excess reagents and byproducts. Furthermore, TFU may be applied to a large variety of nanoparticles as both hydrophobic and hydrophilic filters are available.The two main objectives of this study were: 1) to illustrate the experimental aspects of the TFU approach through an invited video experience and 2) to demonstrate the feasibility of the TFU method for larger volumes of colloidal nanoparticles and smaller volumes of retentate. First, unfuctionalized AgNPs (4 L, 15.2 μg ml -1 ) were synthesized using the well-established Creighton method 22,23 by the reduction of AgNO 3 with NaBH 4 . AgNP polydispersity was then minimized via a 3-step TFU using a 50-nm filter (460 cm 2 ) to remove AgNPs and AgNP-aggregates larger than 50 nm, followed by two 100-kD (200 cm 2 and 20 cm 2 ) filters to concentrate the AgNPs. Representative samples were characterized using transmission electron microscopy, UV-Vis absorption spectrophotometry, Raman spectroscopy, and inductively coupled plasma optical emission spectroscopy. The final retentate consisted of highly concentrated (4 ml, 8,539.9 μg ml -1 ) yet lowly aggregated and homogeneous AgNPs of 1-20 nm in diameter. This corresponds to a silver concentration yield of about 62%. Video LinkThe video component of this article can be found at http://www.jove.com/video/4167/ Protocol Synthesis of Colloidal AgNPsThe reaction mechanism for the Creighton method (slightly modified, inexpensive) 22 is described in great detail in the Supporting information of reference Pavel et.al together with the undesired hydrolysis side-reaction of NaBH 4 at room temperature or higher. 1. Clean all glassware for 12-24 hr in a 10% HNO 3 bath, then for 4-12 hr in a 1.25 M NaOH in 40% ethanol bath, and finally autoclave. Glassware should be rinsed thoroughly a minimum of five times with ultrapure water (17 MΩ or higher) after the acid and base bath steps.

Analytical‐Based Methodologies for Examining the In Vitro Absorption, Distribution, Metabolism, and Elimination (ADME) of Silver Nanoparticles

“…AgNP Characterization—TFF (Spectrum Labs, Inc.) : The original colloidal AgNPs were size‐selected, purified, and concentrated through a KrosFlo Research IIi system equipped with modified polyether ether sulfone (mPES) Midi Kros filter modules (Schematic S1, Supporting Information). Detailed TFF procedures are provided in the previously published work . Briefly, 3 L of colloidal AgNPs − were first passed through a 500 kDa (790 cm 2 , ≈50 nm pore size) membrane filter.…”

“…To address this aspect and to further improve the in vitro extraction, we added a one‐step TFF after CPE. In our previous work, TFF was proven to size‐select, concentrate, and purify either small or large volumes of colloidal AgNPs . TFF is a “green” isolation method, which tangentially pumps the liquid sample containing dissolved (Ag + ) or suspended (AgNPs) particulates through a porous membrane filter of a desired size (1–1000 kDa) .…”

In Vitro Evaluation of Anti‐Aggregation and Degradation Behavior of PEGylated Polymeric Nanogels under In Vivo Like Conditions

“…As one of the main membrane filtration techniques, TFF (or cross flow filtration) has been used for decades to purify and concentrate biotherapeutics in the pharmaceutical industry . Equipped with filters with different MWCO, TFF also enables purification, size selection, and concentration of nanoparticles.…”

Solid Plasmonic Substrates for Breast Cancer Detection by Means of SERS Analysis of Blood Plasma

“…It should be noted, that if the protocol is followed correctly, the final solution should quickly change color from colorless to brown and finally to yellowish grey over the course of 5 min. Once the synthesis process completed, tangential flow filtration (TFF) technique was implemented for the purification and concentration of the NPs, as described in the literature [26,27]. This step turned out to have a major role in the synthesis of suitable substrates for SERS measurements performed on bio-fluids.…”