这项工作得到国家科学基金会的授权MCB-1330685的支持。 DWM承认康奈尔大学分子生物物理学培训基金（NIH T32GM0082567）的部分支持。

小心:使用前请咨询所有相关的材料安全数据表（MSDS）。使用压缩气体时，请使用适当的安全措施，包括适当的校准气体处理调节器和阀门以及认可的气体管道。与液态冷冻剂接触会导致严重的冻伤和坏死。使用适当的个人防护设备（面罩，手套，实验室外套，全长裤，闭式脚趾鞋），所有这些都必须不透液体。保持静置，并确保在使用液体冷冻剂时从设备畅通无阻的出口路径。注意使用压缩气体和液体冷冻剂时的窒息危险，并在通风良好的地方使用充足的补充空气（通风橱或高空气更换率的房间）。 1.用于密度测量的水溶液的制备注意:因为重量更容易测量到高于vol的精度溶液浓度以w / w为单位测量。所有的密度和熔点或沸腾温度都是大气压〜100 kPa。以下步骤描述了35％w / w甘油溶液的制备。对于其他浓度和溶质，可以使用相同的程序。 <ol><li>对于感兴趣的每种溶质类型和浓度，总体估计所需的溶质质量以获得所需的最终浓度（ 例如 ，在25％w / w至100％w / w之间），总溶液体积，V tot = 10mL溶液体积。例如，对于35％w / w甘油溶液（ ρs = 1.26g / mL），溶质质量m s为: <img alt="方程" src="/files/ftp_upload/55761/55761eq1.jpg" /> 其中x是溶质质量分数（0.35）， ρw = 1 g / mL是水的密度。 </li><li>将15 mL离心管（或其他体积校准的不透水容器）放在锅上的分析微量天平。将所需质量的溶质/冷冻保护剂（ 例如 ，3.77g甘油用于35％w / w溶液）分配到管中，并记录实际溶质质量。 </li><li>添加高纯度（&gt; 18MΩ）去离子水，使总质量达到10.0 g </li><li>将容器旋转30秒（用于液体溶质）或5分钟（对于固体溶质），直到溶液光学上均匀。 </li><li>测量和记录解决方案的最终质量。用密封盖密封容器，并保存在恒温（293-298 K）。 </li></ol> 2.样品冷却室的制备<ol><li>将下述实验装置放在外壳中，并将干燥空气（&gt; 5％相对湿度（rh））流入外壳。 注意:外壳可能是一个简单的金属框架，其顶部和三边用透明塑料片密封，并通过第四面用柔性塑料片进行实验访问。穿面罩和全身覆盖物，以尽量减少实验者引入的湿度。水分冷凝和冰的形成可以以几种方式干扰低温温度密度测量，因此必须最小化。 </li><li>将氯丁橡胶盘放在4.5L玻璃杜瓦瓶的底部，以保护杜瓦瓶免受损坏。 </li><li>小心地将高导热铜室（带有密封底部的中空圆筒）插入烧瓶中，直到其放在橡胶盘上。调整从室向外突出到杜瓦墙上的支柱，使得腔室居中并且不会有岩石倾向。 注意:杜瓦瓶将保持液氮，并且体积较小的铜室将容纳液态N 2 -Ar混合物。液氮提供了一个热浴，其将铜室及其内容物保持在77K的恒定温度，并降低了室中的沸腾和蒸发损失。房间＆＃39的小直径抑制可能干扰浮力测量的表面波，并且有助于隔离室内的液体与设备中其他地方形成的霜和冰。 </li><li>将气体管的出口插入干燥的N 2气体，流速为〜2L / min，下降到铜室底部，并吹扫湿气室。 </li><li>将液氮慢慢地倒入杜瓦瓶中，在铜室外面，允许时间进行氮气蒸发。 注意:沸点终止后的最终填充水平应在铜室顶部的约4厘米内。 </li><li>用一个环形泡沫绝缘盖覆盖杜瓦瓶的外部部分。从铜室中取出干燥的N 2气体吹扫管，并插入盖子中的匹配开口。 注意:在杜瓦瓶中从蒸发出的N 2气体与吹扫流的组合排出任何潮湿空气并防止其冷凝和结晶化n冷面。 </li><li>慢慢地将液氮倒入铜室。沸点终止后的最终填充水平应在铜室顶部的约4厘米内。 </li><li>将薄的光学透明塑料薄片放在盖子上的中央开口或排气口上，并将N 2气体流速降低至〜0.2L / min，在低温液体之上的气体空间内留下轻微的N 2气体超压。 注意:只要低温液体存在于杜瓦和室内，根据需要继续调节N 2气体流量，以保持这种超压，防止水分进入杜瓦并形成冰块。 </li></ol> 3. T = 298 K和T = 77 K时测试质量的体积和密度的测定<ol><li>通过将T = 298 K的空气中的〜1 g，〜0.4 mL PTFE质量（ 表材料 ）的表观质量放在锅上的校准分析微量天平。 </li><li>使用气体比重瓶在T = 298 K下确定测试质量的体积V （298 K），或使用卡尺测量尺寸。如果使用尺寸测量，测试质量必须具有简单，精确的形状（无锥形或圆角），并且应确定通孔的体积（对于悬挂线）。 </li><li>通过根据以下方式校正由空气施加的浮力的测量的表观质量来计算测试质量的质量m : <img alt="方程" src="/files/ftp_upload/55761/55761eq2.jpg" /> 其中ρ 空气 = 1.23g / L（〜0.1％校正）。 </li><li>将微量天平放在距离杜瓦瓶大约10厘米的稳定平台上，并验证其校准。使用2毫米（50微米）的单丝线悬挂测试质量，该线条从微量天平下侧的钩子（设计用于悬挂质量测量）和通道gh是测试质量的一个洞。确定空气中的表观质量，并与步骤3.3中的测量值进行比较，根据需要对线的质量进行校正。 </li><li>通过在LN2中测定纯液氮中的表观质量，确定T = 77K时测试质量的体积V （77 K）。将测试质量降低到铜室内的液氮中，直到其完全浸没。当煮沸停止时，测量表观质量。 注意:如果铜室中的液氮静止，微量天平和液面之间的气流最小，则该质量可以测量到大于±0.0002 g的精度。 </li><li>估计线路的淹没部分的浮力，并与测量误差相比较，验证其较小。 </li><li>使用其已知质量m计算77 K下测试质量的体积和密度，并在77 K下测量LN2中的表观质量， m app in LN2，根据以下内容: <img alt="方程" src="/files/ftp_upload/55761/55761eq3.jpg" /> 其中ρLN2（ （77K）= 0.807g / mL。 </li></ol> 4.初始液体N 2 -Ar混合物的制备<ol><li>流量Ar气体以〜2L / min的流速通过盘管连接到其出口。将卷管放置在上支柱的顶部，稳定铜室的位置，恰好在液氮高度和杜瓦顶表面之下。冷N 2和Ar气体会积聚在低温液体之上，热传导，对流和辐射会使管道和Ar气体冷却。 </li><li>在使卷管冷却5分钟后，将管的出口置于铜室中，至少在液氮表面10厘米处。然后用环形盖和透明片覆盖杜瓦。 </li><li>调节Ar流速直到Ar气泡上升从管出口到液氮的顶面。然后降低流速，直到在出口处形成气泡，但在破坏液氮表面之前溶解或液化。 注意:随着铜室中的Ar浓度增加，根据需要定期调节Ar流速以保持气泡形成。如果Ar流速太低，Ar可能在管内冻结并阻塞流动。 </li><li>根据需要添加液氮以保持其周围杜瓦的水平。当冰层积聚在冷面上时，取出冰块。 </li><li>通过将附着在薄绝缘杆上的薄（ 例如 35微米）的铜箔片插入铜室来定期混合液体，并像活塞一样缓慢地上下移动液体。这将降低浓度梯度和Ar从溶液中析出的趋势。 </li></ol> 5.测量和调整初始N 2 -Ar混合物的密度TURE <ol><li>通过估计待测样品的T = 77 K密度计算N 2 -Ar混合物的目标密度， 例如在较高浓度的样品非水性组分下的测量。 </li><li>使用单丝线将测试质量连接到微量天平测量盘下侧的钩子上，测量其在空气中的表观质量，并在步骤3.1中确认与测量一致。 </li><li>混合N 2 -Ar溶液以消除浓度和浓度梯度，如步骤4.5。 </li><li>将测试质量通过将其降低到铜室外的液氮中来将测试质量预冷却到T = 77K。将测试物质提升到液氮以上的氮气冷层中，等待残余液氮从测试物质中蒸发掉，然后将冷，干试验质量降低到N 2 -Ar混合物中直至完全浸没，在液面的2厘米以内。 </li><li&gt;在任何沸腾和表面波消失后，测量测试质量的表观质量。使用其真实质量m和根据以下步骤从步骤3.7计算T = 77K体积V （77K）的溶液密度: <img alt="方程" src="/files/ftp_upload/55761/55761eq4.jpg" /></li><li>通过流动附加的Ar来增加溶液密度，直到获得所需的初始密度。下沉的样品滴很容易丢失，因此初始密度应至少高于预期样品密度的几个百分点。然后样品将浮起来，使其更容易跟踪，并且N 2 -Ar混合物密度将仅需要通过添加液体N 2而向下调整。 </li><li>卸下Ar预冷却的卷管，并允许在下次使用前温热和干燥。 </li></ol> 6.样品溶液冷却滴<ol><li>在滴落和冷却之前，立即重复步骤1.5至mix氮/氩低温液体。小心不要引入任何气泡。 </li><li>取出样品管的密封盖。使用干净的1 mL注射器，提取高达1 mL的溶液，并更换盖子。将27至33 G针头连接到注射器上，然后将少量样品通过针头排出，以排除先前分配的空气和任何残留物。 </li><li> 可以使用两种方法将样品滴入N 2 -Ar混合物。 <ol><li>对于具有较大非水组分浓度（&gt; 45％w / w）的样品，可以以适度的冷却速率进行玻璃化，轻轻按压注射器以移位一个小（250μm至1 mm）的直径，〜10 nL至1μL滴由针尖悬挂在表面张力下。轻轻敲击针头，将液滴向液体N 2 -Ar混合物分液并投射。 </li><li>对于需要更快速冷却玻璃化的样品，将气管的出口连接到真空发生器或（由实验室压缩空气提供）在液体N 2 -Ar混合物上方的气体空间中，并轻轻地吸走形成的冷气层。这样可以提高小样品的冷却速度。 <ol><li>仔细地将针尖接触到25-75μm厚的透明聚合物条，以分配少量的样品（&lt;10nL，相当于液滴直径&lt;200μm）。 注意:为了获得最小，最接近球形，最容易去除的液滴，将该条在疏水性涂层溶液中浸泡10分钟，然后在样品分配前干燥。 </li><li>用连接的塑料或木杆抓住条带，并手动将杆加上条带浸入液体N 2 -Ar混合物中。 </li><li>一旦液滴凝固并且沸腾已经停止，用镊子抓住杆的对面的边缘。将条带弯曲，保持浸没在液体N 2 -Ar中，直到样品滴下来并漂浮到冲浪高手。 </li></ol></li></ol></li></ol> 7.样本状况评估<ol><li>使用长距离工作距离（5-10厘米）的双目显微镜和来自LED或光纤照明器的明亮，凉爽的照明，仔细检查液滴，同时将其浸入液体N 2 -Ar中。玻璃化滴应该清楚12,13 。拒绝浑浊或浑浊的液滴（可能含有多于一个相）和/或显示包括裂纹在内的光学缺陷（可能与改变平均密度的空隙有关）。 注意:绘制铜室的内表面以提供黑色背景，可以方便识别样品的缺陷。 </li></ol> 8.样品密度的测定<ol><li>分配的液滴将首先在N 2 -Ar混合物中浮起，沉入或（很少）中性浮力。浮动液滴有时会受到表面张力，微小气泡或粘附的冰粒的阻碍。用显微镜检查整个液滴表面。使用一个小（直径2-3毫米，长10厘米）的预冷塑料或木棒将液体表面向下放置，并观察其反应。 </li><li>如果液滴下沉，则使用步骤4中的步骤增加液体N 2 -Ar的密度，直到液滴变得中性浮力或漂浮。 </li><li>如果液滴漂浮，则通过使用1.8 mL冷冻管加入液氮来降低液体N 2 -Ar的密度。在大的初始混合密度（1.2-1.3g / mL）下，以1mL增量添加N 2给出明显的密度变化，但是应该在低密度（0.8-0.9g / mL）下向5mL增加。在铜室中上下使用薄的穿孔铜箔片，轻轻混合N 2 -Ar（以免损失样品滴）。 </li><li>每次添加N 2之后，使用小的预冷棒轻轻地将浮动液滴向下移动到液体中，并在其返回到表面时观察其速度。 </li><li>当溶液密度被调整为使得液滴看起来是中性浮力或上升非常缓慢（&lt;50微米/秒将保证〜0.1％或更好的密度精确度下降，体积低至50 pL），测量N 2 - Ar混合物密度，然后加入另外的液体N 2，直到液滴首先开始缓慢下沉，并再次测量N 2 -Ar混合物密度。这两个测量将提供液滴密度的界限。 </li></ol>

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A., Schall, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sample+size:+An+important+parameter+in+flash-cooling+macromolecular+crystallization+solutions.">Sample size: An important parameter in flash-cooling macromolecular crystallization solutions.</a> J. Appl. Cryst. 38 (3), 412-419 (2005).</li><li>Bosart, L. W., Snoddy, A. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Specific+gravity+of+glycerol.">Specific gravity of glycerol.</a> Ind Eng Chem. 20 (12), 1377-1379 (1928).</li><li>Rodrigues, M., Francesconi, A. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+study+of+the+excess+molar+volumes+of+binary+and+ternary+mixtures+containing+water+++(1,2-ethanediol,+or+1,2-propanediol,+or+1,3-propanediol,+or+1,2-butanediol)+++(1-n-butyl-3-methylimidazolium+bromide)+at+298.15+K+and+atmospheric+pressure.">Experimental study of the excess molar volumes of binary and ternary mixtures containing water + (1,2-ethanediol, or 1,2-propanediol, or 1,3-propanediol, or 1,2-butanediol) + (1-n-butyl-3-methylimidazolium bromide) at 298.15 K and atmospheric pressure.</a> J Solution Chem. 40 (11), 1863-1873 (2011).</li><li>Berejnov, V., Husseini, N. S., Alsaied, O. A., Thorne, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+cryoprotectant+concentration+and+cooling+rate+on+vitrification+of+aqueous+solutions.">Effects of cryoprotectant concentration and cooling rate on vitrification of aqueous solutions.</a> J Appl Cryst. 39 (2), 244-251 (2006).</li><li>Meisburger, S. P., Warkentin, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Breaking+the+Radiation+Damage+Limit+with+Cryo-SAXS.">Breaking the Radiation Damage Limit with Cryo-SAXS.</a> Biophys J. 104 (1), 227-236 (2013).</li></ol>

作者没有什么可以披露的。

主要由具有对仪器制造工具和机械的访问限制的本科生开发的本设备和方法仍然为低至50pL的单个液滴提供高精度的密度测量。在接近和高于50％w / w的浓度范围内，其中小的冷却速度足以获得玻璃化样品，其密度与先前对散装样品的测量结果一致。目前密度的外推至0％浓度 - 纯水 - 也与77 K 9的低密度无定形冰的接受密度相当吻合。 根据使给定液滴组成中性?...

水和含水混合物在其各个阶段的物理性质是基本兴趣的，并且对体内和体外对生物系统的理解是重要的。在当代冷冻生物学和生物冷冻保存中，含水冷冻保护剂混合物的玻璃体或非晶相特别令人关注1,2 。冰晶的成核和生长可能破坏细胞和组织，并促进蛋白质变性和聚集，因此使溶剂玻璃化的冷冻保存方案变得越来越受欢迎。在生物分子晶体学中，生物分子之间的通道中溶剂的结晶破坏了晶格并降低了衍射性质。玻璃化通过快速冷却，脱水和加入冷冻保护性溶质如甘油，乙二醇，聚乙二醇（PEG），醇和盐。 玻璃化限制冰结晶和生长，但不能消除所有与冷却有关的样品损伤。例如，当蛋白质晶体冷却到玻璃化状态3时，晶体的马赛克（晶体取向的分布的度量）通常增加10到100倍，玻璃化精子细胞和卵母细胞的解冻后存活率变化很大。 一种损伤机理是冷却3,4,5时溶剂和周围物质的不均匀收缩。晶体，细胞或组织中的平衡溶剂和溶质浓度是温度依赖性的，溶剂加溶质和周围材料可能会以不同的量收缩。快速冷却可能会在玻璃化之前防止溶剂和溶质再分配，并且差异收缩<html>可能导致大的不均匀的非平衡应力，导致样品损坏。 因此，减少冷却诱发的损伤的合理方法可以从对液体和玻璃化含水混合物的温度依赖密度的了解中获益。在溶质浓度超过溶液重量（w / w）的50％以上的溶质浓度下，大多数含水冷冻保护剂混合物可以以10 K / s或更低的适度冷却速率进行玻璃化，从而允许使用大玻璃样品进行生产和密度测量。然后可以使用阿基米德原理，通过测量悬浮在诸如氮气的液体冷冻剂中时样品的表观重量来确定密度。然而，随着溶质浓度的降低，玻璃化所需的冷却速度迅速增加:甘油水溶液的冷却速率从溶液50重量％到溶液体积（mL / w）至&lt;1,000 K时提高至&gt; 1,000 25％w / v的K / sass ="xref"&gt; 7。热传递成为边界层限制，从而实现更大的冷却速度需要更小和更小的样品8 。 纯玻璃水和冰的密度的测量已经通过将真空中的微米直径（femtoliter volume）的液滴沉积到低温冷却的表面上来实现，以便建立宏观（克质量）样品。该样品的密度通过在液氮 - 氩混合物中的低温放置测定，其中调节低温液体的密度直到样品变得中性浮力9 。然而，以最小化空隙体积的方式从大量小滴中产生大量样品 - 这是先前玻璃态相密度测量中重要的误差源 - 是不重要的。对于含水混合物，在气雾化和真空沉积期间溶液组分的差异蒸发可导致沉积浓度的重大不确定性。 我们已经开发了一种基于低温分析法的方法，可以使用小至50 pL 10的各种液滴进行精确的含水混合物密度测定。这些液滴可以快速冷却，同时保持其原始浓度，并且可以使用与X射线衍射测量相关的简单目视测定来评估其低温状态（玻璃化或结晶）。该方法广泛适用于水性和非水性混合物，并且可以扩展到各种生物样品，包括细胞（ 例如茎和卵），组织样品和蛋白质晶体，其低温密度为0.8-1.4g /毫升。

<table><tbody><tr><td>centrifuge tube</td><td>Falcon</td><td>6029236</td><td>15 mL conical centrifuge tube</td></tr><tr><td>glycerol, &gt;99.5%</td><td>Sigma&amp;nbsp;</td><td>G9012-100 mL</td><td></td></tr><tr><td>ethylene glycol, &gt;99.8%</td><td>Sigma</td><td>324558-100 mL</td><td></td></tr><tr><td>analytical microbalance</td><td>Mettler</td><td>AE240</td><td>Analytical balance, 0.01 mg resolution, has hook on bottom for weighing below the balance&amp;nbsp;</td></tr><tr><td>vortexer</td><td>Scientific Industries</td><td>SI-0236</td><td>Vortex-Genie 2</td></tr><tr><td>Apparatus enclosure framing</td><td>Unistrut&amp;nbsp;</td><td>1-5/8&quot; metal framing</td><td>48&quot; wide x 24&quot; deep x 40&quot; tall&amp;nbsp;</td></tr><tr><td>Apparatus enclosure air barrier</td><td></td><td></td><td>any clear plastic sheeting</td></tr><tr><td>neoprene rubber disk</td><td></td><td></td><td>4&quot; diameter, 1/8&quot; thick</td></tr><tr><td>dewar flask</td><td>Scilogix Dilvac</td><td>SS333</td><td>4.5 liter dewar flask with steel case and clamp lid</td></tr><tr><td>copper chamber</td><td></td><td></td><td>This fabricated part is comprised of a 1.43&quot; diameter, 0.017&quot; wall thickness copper tube with a solid cylindrical copper base soldered to seal one end.&amp;nbsp; The copper base is 0.87&quot; tall and the overall chamber height is 7&quot;.</td></tr><tr><td>nitrogen gas</td><td>Airgas</td><td>NI HP300</td><td>99.998% pure N2 gas</td></tr><tr><td>argon gas</td><td>Airgas</td><td>AR HP300</td><td>99.998% pure Ar gas</td></tr><tr><td>rotameter</td><td>Omega</td><td>FL3692ST</td><td>2.52 L/min max flow rate</td></tr><tr><td>foam insulating lid</td><td></td><td></td><td>This part is fabricated from 4 lb/ft&lt;sup&gt;3&lt;/sup&gt; crosslinked polyethylene foam (supplied by Technifab, 1355 Chester Industrial Parkway, Avon, OH), and has an OD of 2.42&quot;, and ID of 1.52&quot;, and a thickness of 0.79&quot;.&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;</td></tr><tr><td>PTFE test mass</td><td></td><td></td><td>This fabricated part is a 0.246&quot; diameter, 0.580&quot; tall cylinder with a 0.060&quot; diameter hole running perpendicular to and intersecting the cylinder axis ~0.10&quot; from one end.&amp;nbsp;</td></tr><tr><td>microbalance platform</td><td>Unistrut</td><td>1-5/8&quot; metal framing</td><td>11&quot; wide x 24&quot; long x 24&quot; high rectangular frame with an top aluminum sheet containing a hole for the monofilament and hanging test mass</td></tr><tr><td>2 mil (50 um) monofilament line</td><td>Berkley</td><td>NF1502-CM</td><td>Nanofil fishing line</td></tr><tr><td>Argon precooling coil tubing</td><td>VWR</td><td>60985-512</td><td>1/8&quot; ID x 1/4&quot; OD PVC tubing</td></tr><tr><td>perforated copper foil mixer</td><td></td><td></td><td>1.4&quot; diameter,&amp;nbsp; 35 micron thick copper disk, cut from 1 ounce/ft&lt;sup&gt;2&lt;/sup&gt; copper sheet and perforated with holes using an awl or other sharp pointed tool.&amp;nbsp; Insert 1-2 mm diameter rigid thermally insulating (plastic or wood) rod into the center and fix using epoxy as needed.</td></tr><tr><td>syringe</td><td>BD</td><td>309628</td><td>1 mL Luer-Lok tip syringe</td></tr><tr><td>vacuum generator</td><td>Gast</td><td>VG-015-00-00</td><td>compressed air venturi single stage vacuum generator</td></tr><tr><td>hydrophobic coating spray</td><td>RainX</td><td>620036</td><td>plastic water repellent</td></tr><tr><td>long focal length stereo microscope</td><td>Bausch and Lomb Stereozoom 6</td><td></td><td>0.67-4 x zoom pod with 20X eyepieces, 10 cm working distance&amp;nbsp;</td></tr><tr><td>LED ring illuminator</td><td>Amscope</td><td>LED144S</td><td></td></tr><tr><td>LED spot illuminator</td><td>Newhouse Lighting</td><td>NHCLP-LED</td><td>3W LED gooseneck clamp lamp</td></tr><tr><td>1.8 ml cryo vial</td><td>Nunc</td><td>V7634-500EA</td><td>Any 1.8 or 2 mL cryovial is adequate</td></tr></tbody></table>

measuring the densities of aqueous glasses at cryogenic temperatures

我们展示了一种确定含水混合物和需要快速冷却的其他样品的玻璃态低温温度密度以制备所需低温温度相的方法。通过投影到液氮 - 氩（N 2 -Ar）混合物来冷却微升至皮升级的液滴。使用与X射线衍射测量相关的视觉测定来评估液滴的低温温度相。通过添加N 2或Ar来调节液体N 2 -Ar混合物的密度，直到液滴变得中性浮力。使用测试质量和阿基米德原理确定该混合物的密度以及因此的液滴密度。在液体制备中适当的注意，管理液体冷冻剂混合物以上的气体以最小化结冰，以及定期混合低温混合物以防止密度分层和相分离，精度至&lt;0.5％的滴度小至50 pL的密度容易确定。水冷冻保护剂混合物的测量提供了对冷冻保护剂作用的了解，并提供定量数据以促进生物冷冻保存中的热收缩匹配。

分别在图 1A和图1B中分别显示了T = 77K下玻璃化甘油水溶液和乙二醇水溶液的密度测量值，以及T = 298 K和77 K之间的比容量的相应变化，确定的T = 298K密度， 如图2所示。在高冷冻保护剂浓度下，溶液在冷却至玻璃化状态时收缩，而纯水膨胀。预测两种冷冻保护剂的近20-25％w / ...

Watch this Scientific Journal Video about Measuring the Densities of Aqueous Glasses at Cryogenic Temperatures at JoVE.com

Measuring the Densities of Aqueous Glasses at Cryogenic Temperatures

描述了一种用于在低温下测定含水混合物的微米到微米级的玻璃体相密度的方案。

在低温下测量水性玻璃的密度

We demonstrate a method for determining the vitreous phase cryogenic temperature densities of aqueous mixtures, and other samples that require rapid ...

measuring-the-densities-of-aqueous-glasses-at-cryogenic-temperatures

Research

JoVE Journal

Engineering

8.6K 次观看.  Cornell University. 描述了一种用于在低温下测定含水混合物的微米到微米级的玻璃体相密度的方案。 

视频: Measuring the Densities of Aqueous Glasses at Cryogenic Temperatures

LabVIEW-operated Novel Nanoliter Osmometer for Ice Binding Protein Investigations

Ice-binding proteins (IBPs), including antifreeze proteins, ice structuring proteins, thermal hysteresis proteins, and ice recrystallization inhibition proteins, are found in cold-adapted organisms and protect them from freeze injuries by interacting with ice crystals. IBPs are found in a variety of organism, including fish1, plants2, 3, arthropods4, 5, fungi6, and bacteria7. IBPs adsorb to the surfaces of ice crystals and prevent water molecules from joining the ice lattice at the IBP adsorption location. Ice that grows on the crystal surface between the adsorbed IBPs develops a high curvature that lowers the temperature at which the ice crystals grow, a phenomenon referred to as the Gibbs-Thomson effect. This depression creates a gap (thermal hysteresis, TH) between the melting point and the nonequilibrium freezing point, within which ice growth is arrested8-10, see Figure 1. One of the main tools used in IBP research is the nanoliter osmometer, which facilitates measurements of the TH activities of IBP solutions. Nanoliter osmometers, such as the Clifton instrument (Clifton Technical Physics, Hartford, NY,) and Otago instrument (Otago Osmometers, Dunedin, New Zealand), were designed to measure the osmolarity of a solution by measuring the melting point depression of droplets with nanoliter volumes. These devices were used to measure the osmolarities of biological samples, such as tears11, and were found to be useful in IBP research. Manual control over these nanoliter osmometers limited the experimental possibilities. Temperature rate changes could not be controlled reliably, the temperature range of the Clifton instrument was limited to 4,000 mOsmol (about -7.5 &deg;C), and temperature recordings as a function of time were not an available option for these instruments.
We designed a custom-made computer-controlled nanoliter osmometer system using a LabVIEW platform (National Instruments). The cold stage, described previously9, 10, contains a metal block through which water circulates, thereby functioning as a heat sink, see Figure 2. Attached to this block are thermoelectric coolers that may be driven using a commercial temperature controller that can be controlled via LabVIEW modules, see Figure 3. Further details are provided below. The major advantage of this system is its sensitive temperature control, see Figure 4. Automated temperature control permits the coordination of a fixed temperature ramp with a video microscopy output containing additional experimental details.
To study the time dependence of the TH activity, we tested a 58 kDa hyperactive IBP from the Antarctic bacterium Marinomonas primoryensis (MpIBP)12. This protein was tagged with enhanced green fluorescence proteins (eGFP) in a construct developed by Peter Davies' group (Queens University)10. We showed that the temperature change profile affected the TH activity. Excellent control over the temperature profile in these experiments significantly improved the TH measurements. The nanoliter osmometer additionally allowed us to test the recrystallization inhibition of IBPs5, 13. In general, recrystallization is a phenomenon in which large crystals grow larger at the expense of small crystals. IBPs efficiently inhibit recrystallization, even at low concentrations14, 15. We used our LabVIEW-controlled osmometer to quantitatively follow the recrystallization of ice and to enforce a constant ice fraction using simultaneous real-time video analysis of the images and temperature feedback from the sample chamber13. The real-time calculations offer additional control options during an experimental procedure. A stage for an inverted microscope was developed to accommodate temperature-controlled microfluidic devices, which will be described elsewhere16.
The Cold Stage System
The cold stage assembly (Figure 2) consists of a set of thermoelectric coolers that cool a copper plate. Heat is removed from the stage by flowing cold water through a closed compartment under the thermoelectric coolers. A 4 mm diameter hole in the middle of the copper plate serves as a viewing window. A 1 mm diameter in-plane hole was drilled to fit the thermistor. A custom-made copper disc (7 mm in diameter) with several holes (500 &mu;m in diameter) was placed on the copper plate and aligned with the viewing window. Air was pumped at a flow rate of 35 ml/sec and dried using Drierite (W.A. Hammond). The dry air was used to ensure a dry environment at the cooling stage. The stage was connected via a 9 pin connection outlet to a temperature controller (Model 3040 or 3150, Newport Corporation, Irvine, California, US). The temperature controller was connected via a cable to a computer GPIB-PCI card (National instruments, Austin, Texas, USA).

Ice binding proteins (IBPs), also known as antifreeze proteins, inhibit ice growth and are a promising additive for use in the cryopreservation of tissues. The main tool used to investigate IBPs is the nanoliter osmometer. We developed a home-designed cooling stage mounted on an optical microscope and controlled using a custom-built LabVIEW routine. The nanoliter osmometer described here manipulated the sample temperature in an ultra-sensitive manner.

LabVIEW操作的新型纳升渗透压仪冰结合蛋白的调查

Ice-binding proteins (IBPs), including antifreeze proteins, ice structuring proteins, thermal hysteresis proteins, and ice recrystallization inhibition ...

科研

化学

Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films

This report aims to fully describe the experimental technique of using ellipsometry for cooling rate dependent Tg (CR-Tg) experiments. These measurements are simple high-throughput characterization experiments, which can determine the glass transition temperature (Tg), average dynamics, fragility and the expansion coefficient of the super-cooled liquid and glassy states for a variety of glassy materials. This technique allows for these parameters to be measured in a single experiment, while other methods must combine a variety of different techniques to investigate all of these properties. Measurements of dynamics close to Tg are particularly challenging. The advantage of cooling rate dependent Tg measurements over other methods which directly probe bulk and surface relaxation dynamics is that they are relatively quick and simple experiments, which do not utilize fluorophores or other complicated experimental techniques. Furthermore, this technique probes the average dynamics of technologically relevant thin films in temperature and relaxation time (&#964;&#945;) regimes relevant to the glass transition (&#964;&#945; &#62; 100 sec). The limitation to using ellipsometry for cooling rate dependent Tg experiments is that it cannot probe relaxation times relevant to measurements of viscosity (&#964;&#945; &#60;&#60; 1 sec). Other cooling rate dependent Tg measurement techniques, however, can extend the CR-Tg method to faster relaxation times. Furthermore, this technique can be used for any glassy system so long as the integrity of the film remains throughout the experiment.

Here, we present a protocol for cooling rate dependent ellipsometry experiments, which can determine the glass transition temperature (Tg), average dynamics, fragility and the expansion coefficient of the super-cooled liquid and glass for a variety of glassy materials.

冷却率相关的椭偏仪测量确定薄膜玻膜的动力学

This report aims to fully describe the experimental technique of using ellipsometry for cooling rate dependent Tg (CR-Tg) experiments. These measurements ...

A Simple Dewar/Cryostat for Thermally Equilibrating Samples at Known Temperatures for Accurate Cryogenic Luminescence Measurements

The design and operation of a simple liquid nitrogen Dewar/cryostat apparatus based upon a small fused silica optical Dewar, a thermocouple assembly, and a CCD spectrograph are described. The experiments for which this Dewar/cryostat is designed require fast sample loading, fast sample freezing, fast alignment of the sample, accurate and stable sample temperatures, and small size and portability of the Dewar/cryostat cryogenic unit. When coupled with the fast data acquisition rates of the CCD spectrograph, this Dewar/cryostat is capable of supporting cryogenic luminescence spectroscopic measurements on luminescent samples at a series of known, stable temperatures in the 77-300 K range. A temperature-dependent study of the oxygen quenching of luminescence in a rhodium(III) transition metal complex is presented as an example of the type of investigation possible with this Dewar/cryostat. In the context of this apparatus, a stable temperature for cryogenic spectroscopy means a luminescent sample that is thermally equilibrated with either liquid nitrogen or gaseous nitrogen at a known measureable temperature that does not vary (&#916;T &#60; 0.1 K) during the short time scale (~1-10 sec) of the spectroscopic measurement by the CCD. The Dewar/cryostat works by taking advantage of the positive thermal gradient dT/dh that develops above liquid nitrogen level in the Dewar where h is the height of the sample above the liquid nitrogen level. The slow evaporation of the liquid nitrogen results in a slow increase in h over several hours and a consequent slow increase in the sample temperature T over this time period. A quickly acquired luminescence spectrum effectively catches the sample at a constant, thermally equilibrated temperature.

A simple liquid nitrogen Dewar/cryostat apparatus comprised of a small fused silica optical Dewar, a thermocouple, and a charge-coupled device (CCD) spectrograph are described. The experiments for which this Dewar/cryostat is designed require fast sample loading, freezing, and alignment, accurate and stable sample temperatures, and small size/portability.

一个简单的杜瓦瓶/低温恒温器的热的样品配平在为准确低温发光测量已知温度

The design and operation of a simple liquid nitrogen Dewar/cryostat apparatus based upon a small fused silica optical Dewar, a thermocouple assembly, and ...

工程学

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable 57Fe isotope, namely M&#246;ssbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe2.85Co1)77Mo8Cu1B14 MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. M&#246;ssbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of M&#246;ssbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

结构转换的原位和原位研究方法: 金属玻璃结晶的实例

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic ...

Biological Samples Preparation for Speciation at Cryogenic Temperature using High-Resolution  X-Ray Absorption Spectroscopy

The study of elements with X-ray absorption spectroscopy (XAS) is of particular interest when studying the role of metals in biological systems. Sample preparation is a key and often complex procedure, particularly for biological samples. Although X-ray speciation techniques are widely used, no detailed protocol has been yet disseminated for users of the technique. Further, chemical state modification is of concern, and cryo-based techniques are recommended to analyze the biological samples in their near-native hydrated state to provide the maximum preservation of chemical integrity of the cells or tissues. Here, we propose a cellular preparation protocol based on cryo-preserved samples. It is demonstrated in a high energy resolution fluorescence detected X-ray absorption spectroscopy study of selenium in cancer cells and a study of iron in phytoplankton. This protocol can be used with other biological samples and other X-ray techniques that can be damaged by irradiation.

This protocol presents a detailed procedure to prepare biological cryosamples for synchrotron-based X-ray absorption spectroscopy experiments. We describe all the steps required to optimize sample preparation and cryopreservation with examples of the protocol with cancer and phytoplankton cells. This method provides a universal standard of sample cryo-preparation.

使用高分辨率X射线吸收光谱在低温下制备生物样品以进行形态分析

The study of elements with X-ray absorption spectroscopy (XAS) is of particular interest when studying the role of metals in biological systems. Sample ...

A Microfluidic Approach for the Study of Ice and Clathrate Hydrate Crystallization

An accurate mechanistic description of water crystallization is challenging and requires a few key elements: superb temperature control to allow the formation of single microscopic crystals and a suitable microscopy system coupled to the cold stage. The method described herein adds another important feature that includes exchanging solutions around ice and clathrate hydrate crystals. The described system comprises a combination of unique and home-developed instruments, including microfluidics, high-resolution cold stages, and fluorescence microscopy. The cold stage was designed for microfluidic devices and allows for the formation of micron-sized ice/hydrate crystals inside microfluidic channels and the exchange of solutions around them. The temperature resolution and stability of the cold stage is one millikelvin, which is crucial for controlling the growth of these small crystals. This diverse system is used to study the different processes of ice and hydrate crystallization and the mechanism by which the growth of these crystals is inhibited. The protocol describes how to prepare microfluidic devices, how to grow and control microscopic crystals in the microfluidic channels, and how the utilization of the flow of liquids around ice/hydrate crystals affords new insights into the crystallization of water.

The present protocol describes the crystallization of microscopic ice crystals and clathrate hydrates in microfluidic devices, enabling liquid exchange around the formed crystals. This provides unparalleled possibilities to examine the crystallization process and binding mechanisms of the inhibitors.

一种用于研究冰和包合物水合物结晶的微流控方法

An accurate mechanistic description of water crystallization is challenging and requires a few key elements: superb temperature control to allow the ...

A Simple and Inexpensive Method for Determining Cold Sensitivity and Adaptation in Mice

Cold hypersensitivity is a serious clinical problem, affecting a broad subset of patients and causing significant decreases in quality of life. The cold plantar assay allows the objective and inexpensive assessment of cold sensitivity in mice, and can quantify both analgesia and hypersensitivity. Mice are acclimated on a glass plate, and a compressed dry ice pellet is held against the glass surface underneath the hindpaw. The latency to withdrawal from the cooling glass is used as a measure of cold sensitivity.
Cold sensation is also important for survival in regions with seasonal temperature shifts, and in order to maintain sensitivity animals must be able to adjust their thermal response thresholds to match the ambient temperature. The Cold Plantar Assay (CPA) also allows the study of adaptation to changes in ambient temperature by testing the cold sensitivity of mice at temperatures ranging from 30 &#176;C to 5 &#176;C. Mice are acclimated as described above, but the glass plate is cooled to the desired starting temperature using aluminum boxes (or aluminum foil packets) filled with hot water, wet ice, or dry ice. The temperature of the plate is measured at the center using a filament T-type thermocouple probe. Once the plate has reached the desired starting temperature, the animals are tested as described above.
This assay allows testing of mice at temperatures ranging from innocuous to noxious. The CPA yields unambiguous and consistent behavioral responses in uninjured mice and can be used to quantify both hypersensitivity and analgesia. This protocol describes how to use the CPA to measure cold hypersensitivity, analgesia, and adaptation in mice.

The Cold Plantar Assay (CPA) measures cold responsiveness between 30 &#176;C and 5 &#176;C, and can also measure cold adaptation. This protocol describes how to use the CPA to measure cold hypersensitivity, analgesia, and adaptation in mice.

测定冷灵敏度和适应小鼠一种简单廉价的方法

Cold hypersensitivity is a serious clinical problem, affecting a broad subset of patients and causing significant decreases in quality of life.  The cold ...

神经科学

从固结 SnSe 颗粒生产 CdSe-SnSe 纳米复合材料

Solution&#45;Processed, Surface&#45;Engineered, Polycrystalline CdSe&#45;SnSe Exhibiting Low Thermal Conductivity

In recent years, solution processes have gained considerable traction as a cost-effective and scalable method to produce high-performance thermoelectric materials. The process entails a series of critical steps: synthesis, purification, thermal treatments, and consolidation, each playing a pivotal role in determining performance, stability, and reproducibility. We have noticed a need for more comprehensive details for each of the described steps in most published works. Recognizing the significance of detailed synthetic protocols, we describe here the approach used to synthesize and characterize one of the highest-performing polycrystalline p-type SnSe. In particular, we report the synthesis of SnSe particles in water and the subsequent surface treatment with CdSe molecular complexes that yields CdSe-SnSe nanocomposites upon consolidation. Moreover, the surface treatment inhibits grain growth through Zenner pinning of secondary phase CdSe nanoparticles and enhances defect formation at different length scales. The enhanced complexity in the CdSe-SnSe nanocomposite microstructure with respect to SnSe promotes phonon scattering and thereby significantly reduces the thermal conductivity. Such surface engineering provides opportunities in solution processing for introducing and controlling defects, making it possible to optimize the transport properties and attain a high thermoelectric figure of merit.

作者聚焦:使用纳米复合材料作为加工热电材料推进能源解决方案

CdSe-SnSe nanocomposites are produced by consolidating surface-engineered SnSe particles. A simple aqueous synthesis is employed to produce SnSe particles. Coating SnSe particles with CdSe molecular complexes allows for controlling grain size and increasing the number of defects present in the nanocomposite, thus lowering the thermal conductivity.

溶液处理、表面工程、多晶 CdSe-SnSe，具有低导热性

In recent years, solution processes have gained considerable traction as a cost-effective and scalable method to produce high-performance thermoelectric ...

在低温下测量水性玻璃的密度

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使用高分辨率X射线吸收光谱在低温下制备生物样品以进行形态分析

一种用于研究冰和包合物水合物结晶的微流控方法

测定冷灵敏度和适应小鼠一种简单廉价的方法

溶液处理、表面工程、多晶 CdSe-SnSe，具有低导热性

溶液处理、表面工程、多晶 CdSe-SnSe，具有低导热性

溶液处理、表面工程、多晶 CdSe-SnSe，具有低导热性