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Lenses designed for 2P microscopy might help here.  They tend to have more
IR correction.  Olympus' XLUMPLFLN or LUMP/IR water dipping lenses are an
example.  I think most manufacturers have similar lenses.  You will probably
need to tweak your collection optics however.  The good news is that PMTs
are fairly tolerant of beam focus differences...  The bad news is that your
confocal pinhole isn't, and for longer wavelengths you will need to open it
up anyway.

On a related note, I'm waiting for somebody to use a Cr:Forsterite laser to
do 2 photon with these NIR dyes.  Cr:Forsterite is similar to Ti:Saph, but
at 1200-1300nm so it can 2P excite dyes that are further into the NIR.  The
main limit right now seems to be in the optics.

Craig


On Mon, Jul 25, 2011 at 9:38 PM, George McNamara
<[log in to unmask]>wrote:

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>
> Hi Claude,
>
> Li-Cor's Odyssey scanner uses APDs. Many FCS confocal microscopes use APDs
> - but not necessarily the filter set(s) for fluorophores such as IRDye800
> (or more clinically, ICG). As for PMTs in the IR: if they have low quantum
> efficiency but the specimen has practically no autofluorescence (and no
> non-specific fluorescence of the NIRF), SNR may approach #/0. On the other
> hand, infrachromatic [yes, this is a word] correction may be poor (or good),
> depending on make and model of microscope and especially objective lens --
> not a big deal if you are only looking at one fluorophore. Most back
> illuminated CCD's have nice QE's in the NIR.
>
> Enjoy,
>
>
> George
> p.s. while looking up infrachromatic on the Internet I came across
> http://iopscience.iop.org/**0036-021X/66/3/R04<http://iopscience.iop.org/0036-021X/66/3/R04>   which reminded me that multiphoton imaging has been around for well over
> a century. I wonder whether more images were acquired that way or by cameras
> and PMTs, APDs etc.  I am not going to trade in my Chameleon or APDs for a
> bucket of supersensitizer, but figured worth mentioning at least one
> alternative has existed for a lng time.
>
>
>
> On 7/25/2011 10:19 PM, Claude Messier wrote:
>
>> *****
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>>
>> I have been using Alexa 680 and Li-Cor IrDye800 for regular fluorescence
>> microscopy. I am trying to migrate infra-red dyes to confocal systems
>> particularly the single-photon variety using spectral detection with a
>> photomultiplier tube detection. Two problems are obvious the laser source
>> and the sensitivity of the photomultiplier tube in the infra-red region.
>> Typical
>> photomultiplier tubes detector have low recovery when approaching 800nm
>> so that is a problem. There are infra-red diode lasers close enough to the
>> excitation peak of IrDye800 to be useable.
>> My question is: has anyone experimented with these infra-red dyes in
>> spectral detection system. Any information that would indicate that this
>> is
>> possible would be appreciated - most important is whether PMT's can
>> recover
>> enough photons at the infra-red end of the sensitivity.
>> Many thanks
>>
>>
>>
>
>
> --
>
>
> George McNamara, PhD
> Analytical Imaging Core Facility
> University of Miami
>