使用Newtonsoft。Json，你可以这样做

JsonConvert.SerializeObject(DateTime.UtcNow)

例如:https://dotnetfiddle.net/O2xFSl

我将使用XmlConvert:

XmlConvert.ToString(DateTime.UtcNow, XmlDateTimeSerializationMode.RoundtripKind);

它会自动保存时区。

DateTime.UtcNow.ToString("s")

返回类似2008-04-10T06:30:00的内容

UtcNow显然返回UTC时间，所以在以下情况下没有伤害:

string.Concat(DateTime.UtcNow.ToString("s"), "Z")

你可以用下面的代码得到“Z”(ISO 8601 UTC):

Dim tmpDate As DateTime = New DateTime(Now.Ticks, DateTimeKind.Utc)
Dim res as String = tmpDate.toString("o") '2009-06-15T13:45:30.0000000Z

原因如下:

ISO 8601有一些不同的格式:

DateTimeKind。当地的

2009-06-15T13:45:30.0000000-07:00

DateTimeKind。Utc

2009-06-15T13:45:30.0000000Z

DateTimeKind。未指明的

2009-06-15T13:45:30.0000000

.NET为我们提供了一个包含这些选项的枚举:

'2009-06-15T13:45:30.0000000-07:00
Dim strTmp1 As String = New DateTime(Now.Ticks, DateTimeKind.Local).ToString("o")

'2009-06-15T13:45:30.0000000Z
Dim strTmp2 As String = New DateTime(Now.Ticks, DateTimeKind.Utc).ToString("o")

'2009-06-15T13:45:30.0000000
Dim strTmp3 As String = New DateTime(Now.Ticks, DateTimeKind.Unspecified).ToString("o")

注意:如果你将Visual Studio 2008的“watch utility”应用到toString(“o”)部分，你可能会得到不同的结果，我不知道这是否是一个bug，但在这种情况下，如果你正在调试，使用String变量会得到更好的结果。

来源:标准日期和时间格式字符串(MSDN)

The "s" standard format specifier represents a custom date and time format string that is defined by the DateTimeFormatInfo.SortableDateTimePattern property. The pattern reflects a defined standard (ISO 8601), and the property is read-only. Therefore, it is always the same, regardless of the culture used or the format provider supplied. The custom format string is "yyyy'-'MM'-'dd'T'HH':'mm':'ss". When this standard format specifier is used, the formatting or parsing operation always uses the invariant culture.

-来自MSDN

如果你在SharePoint 2010或更高版本下开发，你可以使用

using Microsoft.SharePoint;
using Microsoft.SharePoint.Utilities;
...
string strISODate = SPUtility.CreateISO8601DateTimeFromSystemDateTime(DateTime.Now)