你可以使用$。

插入字符串: 用于构造字符串。插值字符串看起来像包含插值表达式的模板字符串。插值后的字符串返回一个字符串，该字符串将其包含的插值表达式替换为它们的字符串表示形式。该特性在c# 6及更高版本中可用。

string commentor = $"<span class=\"fa fa-plus\" aria-hidden=\"true\"> {variable}</span>";

在双引号前加一个反斜杠(\)。这应该有用。

所以你本质上是问如何存储双引号在一个字符串变量?有两个解决方案:

var string1 = @"""inside quotes""";
var string2 = "\"inside quotes\"";

为了让大家更清楚发生了什么:

var string1 = @"before ""inside"" after";
var string2 = "before \"inside\" after";

在c# 11.0预览版中，你可以使用原始字符串字面值。

Raw string literals are a new format for string literals. Raw string literals can contain arbitrary text, including whitespace, new lines, embedded quotes, and other special characters without requiring escape sequences. A raw string literal starts with at least three double-quote (""") characters. It ends with the same number of double-quote characters. Typically, a raw string literal uses three double quotes on a single line to start the string, and three double quotes on a separate line to end the string.

string str = """
    "How to add double quotes"
    """;

<i class=\"fa fa-check-circle\"></i>"与Eval()数据绑定的三元运算符一起使用:

Text = '<%# Eval("bqtStatus").ToString()=="Verified" ? 
       Convert.ToString("<i class=\"fa fa-check-circle\"></i>") : 
       Convert.ToString("<i class=\"fa fa-info-circle\"></i>"

如果我理解你的问题，也许你可以试试这个:

string title = string.Format("<div>\"{0}\"</div>", "some text");