Microscopy Filter Cubes with Pre-Installed Fluorescence Filters

Click to Enlarge
Figure 1.1  Thorlabs' filter cubes feature labels for identifying installed filters.

Features

• Drop-in Filter Cubes with Pre-Installed Fluorescence Filter Sets for Select Nikon and Olympus Microscopes (See Table 1.4)
• Filters Optimized for Common Fluorophores (See Table 1.2)
• Pre-Installed Filters Minimize Handling of Bare Optics
• Durable Aluminum Filter Cube Body
• Side Labels for Marking Installed Filters

This page offers Thorlabs' microscope filter cubes with pre-installed fluorescence filter sets. Choose from 13 available imaging filter sets; each is optimized for a specific fluorophore (see Table 1.2 for options) though they may also be used with other fluorophores. Four filter cube body options are available for each filter set; they are compatible with select Olympus and Nikon fluorescence microscopes (see the Table 1.4 for microscope compatibility). 

Thorlabs also sells additional filters and imaging filter sets that are compatible with the cubes sold on this page. For users who already have imaging filter sets, we also provide empty microscope filter cube bodies. Pre-mounted filter cubes using any of our stock filters can be requested by contacting techsupport@thorlabs.com.

Filter Design
Our filters are manufactured to high-performance optical specifications and designed for durability. They are produced via multiple dielectric layers deposited on a high-precision, fused silica substrate. The substrate is ground and polished to ensure that the highest possible image quality is maintained. The resulting hard-coated optics consist of filter layers that are denser than those obtained from electron beam deposition techniques, and which reduce water absorption while greatly enhancing durability, stability, and performance of the filter. Each filter layer is monitored during growth to ensure minimal deviation from design specification thickness, ensuring overall high-quality filter performance.

Microscopy Filter Cubes
These cubes feature a spring plate retention mechanism for the dichroic mirror that results in lower optic stress for improved imaging. Our design also offers an all-aluminum cube body, simplified optic mounting, and three labels for writing information about installed filters. Each cube is also engraved with the empty cube item number. Refer to Table 1.4 to view which filter cubes are compatible with which microscope.

Although one filter set is pre-installed into each filter cube, users can easily swap the installed filters. The cubes are compatible with the following filters: one excitation filter (Ø25 mm, up to 5 mm thick), one emission filter (Ø25 mm, up to 3.5 mm thick), and one dichroic mirror (up to 25.2 mm x 36.0 mm x 1.1 mm). Optics can be mounted, aligned, and swapped out easily as illustrated in Video 1.3. For detailed assembly instructions, please refer to the assembly manuals in Table 1.4.

When these cubes are placed in a filter cube turret, it is important to balance the weight. To ensure longevity of a motorized filter cube turret and prevent unnecessary wear, please place filter cubes opposing each other to maintain balance.

Filter Set Item #	Fluorophore	Filter Type	Center Wavelength	FWHM	Reflection Band	Transmission Band	AR Coatinga	Transmission Datab
MDF-BFP	BFP	Excitation	390 nm	18 nm	-	-	-
		Emission	460 nm	60 nm	-	-	-
		Dichroic	-	-	360 - 407 nm	425 - 575 nm	Rabs < 2% from 400 to 800 nm
MDF-CFP	CFP	Excitation	434 nm	17 nm	-	-	-
		Emission	479 nm	40 nm	-	-	-
		Dichroic	-	-	423 - 445 nm	460 - 610 nm	Rabs < 2% from 400 to 800 nm
MDF-WGFP	Wild Type GFP	Excitation	445 nm	45 nm	-	-	-
		Emission	510 nm	42 nm	-	-	-
		Dichroic	-	-	415 - 470 nm	490 - 720 nm	Rabs < 2% from 400 to 800 nm
MDF-GFP	GFP	Excitation	469 nm	35 nm	-	-	-
		Emission	525 nm	39 nm	-	-	-
		Dichroic	-	-	452 - 490 nm	505 - 800 nm	Rabs < 2% from 400 to 800 nm
MDF-FITC	FITC	Excitation	475 nm	35 nm	-	-	-
		Emission	530 nm	43 nm	-	-	-
		Dichroic	-	-	470 - 490 nm	508 - 675 nm	Rabs < 2% from 400 to 800 nm
MDF-GFP2	GFP Alexa Fluor® 488	Excitation	482 nm	18 nm	-	-	-
		Emission	520 nm	28 nm	-	-	-
		Dichroic	-	-	350 - 488 nm	502 - 950 nm	-
MDF-YFP	YFP	Excitation	497 nm	16 nm	-	-	-
		Emission	535 nm	22 nm	-	-	-
		Dichroic	-	-	490 - 510 nm	520 - 700 nm	-
MDF-TOM	tdTomato	Excitation	531 nm	40 nm	-	-	-
		Emission	593 nm	40 nm	-	-	-
		Dichroic	-	-	350 - 555 nm	569 - 950 nm	-
MDF-TRITC	TRITC	Excitation	542 nm	20 nm	-	-	-
		Emission	620 nm	52 nm	-	-	-
		Dichroic	-	-	525 - 556 nm	580 - 650 nm	Rabs < 2% from 400 to 800 nm
MDF-TXRED	Texas Red	Excitation	559 nm	34 nm	-	-	-
		Emission	630 nm	69 nm	-	-	-
		Dichroic	-	-	533 - 580 nm	595 - 800 nm	Rabs < 2% from 400 to 800 nm
MDF-MCHC	mCherry	Excitation	562 nm	40 nm	-	-	-
		Emission	641 nm	75 nm	-	-	-
		Dichroic	-	-	350 - 585 nm	601 - 950 nm	-
MDF-CY3.5	Cyanine (CY3.5)	Excitation	565 nm	24 nm	-	-	-
		Emission	620 nm	52 nm	-	-	-
		Dichroic	-	-	533 - 580 nm	595 - 800 nm	Rabs < 2% from 400 to 800 nm
MDF-MCHA	mCherry	Excitation	578 nm	21 nm	-	-	-
		Emission	641 nm	75 nm	-	-	-
		Dichroic	-	-	350 - 588 nm	603 - 950 nm	-

• Select dichroics have an AR coating designed for 45° AOI on the back surface.
• Click on for a plot and downloadable data.

Click to Enlarge
Figure 3.1  Schematic of light passing through a fluorescence microscope.

Click to Enlarge
Figure 3.2  MDF-YFP filter set transmission graph. Note the dichroic mirror (green) reflects light in the excitation wavelength range (blue), and transmits light in the emission wavelength range (green).

Filters for Fluorescence Microscopy

Fluorophores
A fluorophore is a molecule or portion of a molecule that is capable of producing fluorescence. When light of the appropriate frequency necessary to excite a molecule from its ground state to an excited state is present, excitation will occur. However, once in an excited state, the molecule will be unstable. After some short period of time (typically 10^-15 to 10^-9 s), a photon will be released, thereby enabling the molecule to return to a lower energy state. The emitted radiation will be at a longer wavelength (lower energy) than the absorbed radiation due to the loss of energy through various mechanisms such as vibrations, sound, and thermal energy. 

A single fluorophore can be continually excited unless it is destroyed by photobleaching (i.e. the nonreversible destruction of a fluorophore due to photon-induced chemical damage or covalent modification). The average number of excitation and emission cycles that a particular fluorophore can undergo prior to photobleaching depends on its molecular structure and the local environment; some fluorophores bleach quickly after emitting only a few photons while others are far more robust and can undergo thousands or even millions of cycles before bleaching occurs.

Filters for Fluorescence Microscopy
The experimental setup in Figure 3.1 shows the typical filters used for epi-fluorescence microscopy, a form of microscopy in which both the excitation and emission light travel through the microscope objective. By carefully choosing the appropriate filters and mirrors for a given application, the signal-to-noise ratio can be maximized. As shown in Figure 3.1, three types of filters are used to maximize the fluorescence signal while minimizing the unwanted radiation. Each optical element is discussed below.

Excitation Filter
The excitation filter only allows a narrow band of wavelengths to pass through it, around the peak fluorophore excitation wavelength. For example, as shown in Figure 3.2, the bandpass region corresponding to greater than 90% transmission for the Yellow Fluorescent Protein (YFP) Excitation Filter (MF497-16) is 489 - 505 nm; incident radiation outside of this range is either partially (for regions near the transmission region) or totally (for regions further from the bandpass region) blocked by the filter.

Dichroic Mirror
Dichroic mirrors are designed to reflect light whose wavelength is below a specific value (i.e. the cutoff wavelength) while permitting all other wavelengths to pass through it unaltered. In a microscope, the dichroic mirror directs the proper wavelength range to the sample as well as to the image plane. The cutoff wavelength value associated with each mirror indicates the wavelength that corresponds to 50% transmission. For example, as shown in Figure 3.2, the cutoff wavelength for the Yellow Fluorescent Protein (YFP) Dichroic Mirror (MD515) is ~515 nm. The Specs tab provides information on wavelength ranges corresponding to ≥ 90% average reflectance and transmission for each type of dichroic mirror.

By placing one of these mirrors into the experimental setup at 45° with respect to the incident radiation, the excitation radiation (shown in blue in Figure 3.1) is reflected off of the surface of the dichroic mirror and directed towards the sample and microscope objective, while the fluorescence emanating from the sample (shown in red in Figure 3.1) passes through the mirror to the detection system.

Although dichroic mirrors play a crucial role in fluorescence microscopy, they are not perfect when it comes to blocking unwanted light; typically, ~90% of the light at wavelengths below the cutoff wavelength value are reflected and ~90% of the light at wavelengths above this value are transmitted by the dichroic mirror. Hence, some of the excitation light can be transmitted through the dichroic mirror along with the longer wavelength fluorescence emitted by the sample. To prevent this unwanted light from reaching the detection system, an emission filter is used in addition to the dichroic mirror.

Emission Filter
An emission filter serves the purpose of allowing the desirable fluorescence from the sample to reach the detector while blocking unwanted traces of excitation light. Like the excitation filter, this filter only allows a narrow band of wavelengths to pass through it, around the peak fluorophore emission wavelength. For example, as shown in Figure 3.2, the bandpass region corresponding to greater than 90% transmission for the Yellow Fluorescent Protein (YFP) Emission Filter (MF535-22) is 524 - 546 nm; incident radiation outside of this range is either partially (for regions near the transmission region) or totally (for regions further from the bandpass region) blocked by the filter.