Quantification of reagent mixing in liquid flow cells for Liquid Phase-TEM

High-Resolution Bulgeless Liquid-Cell Electron Microscopy

“…Liquid-cell electron microscopy (LCEM) [1][2][3][4][5][6][7] is a known state-of-the-art technique used to perform high-magnification imaging of nanomaterials and biological specimens which are suspended in a liquid inside of a nanofluidic cell (NFC). There are two types of LCEM systems; those connected to a syringe pump and capable of conferring liquid flow, commonly known as 'flow LCEM systems' [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] , and those which are stationary systems [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] herein referred to as 'static LCEM systems'. Current LCEM technology is limited in its ability to precisely control the effective thickness of the liquid layer.…”

The effect of flow on radiolysis in liquid phase-TEM flow cells

“…In the so-called 'bathtub' configuration, the microchips are immersed into an oversized flow channel and the liquid exchange in the LFC, and thus in the imaging area, is achieved mainly by diffusion [37,38]. In the second setup which is often referred to as 'nanofluidic', all the flow is forced into the nanochannel and liquid exchange in the imaging area is dominated by convection [35,38]. Recently it was shown that solutionexchange (due to diffusion) in a 'bathtub' setup is very slow and thus can hardly be utilised for liquid replenishment in the imaging area [38]; in an ideal 'nanofluidic' configuration, however, the linear flow velocity in the nanochannel can reach 1 μm/μs (according to information provided by the manufacturer) which is promising for efficient flushing of radiolytic species [18].…”

“…The flow type, either turbulent or laminar, can be estimated by the characteristic Reynold number, which when being below ∼2100 will indicate a laminar flow [43]. In typical microfluidic scenarios including LP-TEM cells, the Reynolds number is well below 1 [38], indicating laminar flow (see Supporting Information section 1 for details).…”

“…Q is a volumetric flow rate; v¯= Q/A is an average flow velocity derived from the cross-section A of the flow channel. Equation 2 describes a parabolic velocity profile with the maximum flow velocity, v max , in the middle of the channel equal to 3/2 of the average velocity, v. ¯The relation between vā nd the experimental parameter Q can be established by 3D finite elements simulations based on the real geometry for every setup [38]. Since volumetric flow is obsolete for 2D geometry, we will focus on the more general parameter v¯at the inlet later in the text.…”

“…All setups are based on microchips being allocated in the tip of a microfluidic TEM sample holder and can be categorised in two classes based on the way how the flow is directed. In the so-called 'bathtub' configuration, the microchips are immersed into an oversized flow channel and the liquid exchange in the LFC, and thus in the imaging area, is achieved mainly by diffusion [37,38]. In the second setup which is often referred to as 'nanofluidic', all the flow is forced into the nanochannel and liquid exchange in the imaging area is dominated by convection [35,38].…”